Fix OOXML schema validity, correctness, perf, and security issues (#30)

Correctness:
- Tables: derive column count from the rowspan grid so cells in later,
  wider rows are no longer silently dropped
- Tables: thread FootnoteIndex/BookmarkId through per-cell contexts and
  seed FootnoteIndex from the existing part, so footnote and bookmark IDs
  no longer collide across cells or across Build calls
- Emit w:rPr and w:tcPr children in OOXML schema order; previously the
  output was schema-invalid and only tolerated by Word
- Cell margins emit w:left/w:right instead of the invalid w:start/w:end
- ColorParser: accept percentage and decimal rgb()/rgba() components
- vertical-align is matched case-insensitively
- word-spacing no longer doubles letter-spacing
- @page: match the closing brace and skip nested margin-box rules so
  sibling declarations (margin/size) are not lost

Performance:
- Parse each element's inline style once instead of twice
- Allocate list numbering IDs from the threaded NextNumId counter rather
  than rescanning the numbering part per list (O(m^2) -> O(m))
- Compute ordered-list item indices in a single pass (O(n^2) -> O(n))

Security:
- Image fetch: disable auto-redirect and re-check each redirect hop
  against the image policy (closes a SafeDomains/SSRF bypass), cap the
  response size, set a timeout, and parse width/height with
  InvariantCulture

Tests:
- Add rowspan, footnote-id, bookmark-id, and OpenXmlValidator round-trip
  tests, plus rgb() percentage cases
- Regenerate affected verified baselines (structural reordering only;
  rendered text/image output unchanged)

Author: SimonCropp

src/OpenXmlHtml.Tests/ColorParserTests.cs

@@ -16,6 +16,10 @@ public class ColorParserTests
     [TestCase("rgba(0, 128, 0, 1)", "008000")]
     [TestCase("rgba(0,0,255,0)", "0000FF")]
     [TestCase("rgba(100, 200, 50, 0.8)", "64C832")]
+    [TestCase("rgb(100%, 0%, 0%)", "FF0000")]
+    [TestCase("rgb(0%, 100%, 0%)", "00FF00")]
+    [TestCase("rgba(0%, 0%, 100%, 0.5)", "0000FF")]
+    [TestCase("rgb(255.0, 0, 0)", "FF0000")]
     public void ValidColors(string input, string expected) =>
         Assert.That(ColorParser.Parse(input), Is.EqualTo(expected));
 

src/OpenXmlHtml.Tests/Samples/WordSamples.EmployeeOnboardingGuide.DotNet.verified.docx

@@ -2,4 +2,4 @@
 <w:p xmlns:w="http://schemas.openxmlformats.org/wordprocessingml/2006/main"><w:r><w:t xml:space="preserve">All systems </w:t></w:r><w:r><w:rPr><w:b /><w:color w:val="008000" /></w:rPr><w:t xml:space="preserve">operational</w:t></w:r><w:r><w:t xml:space="preserve">.</w:t></w:r></w:p>
 <w:p xmlns:w="http://schemas.openxmlformats.org/wordprocessingml/2006/main"><w:r><w:t xml:space="preserve">● </w:t></w:r><w:r><w:t xml:space="preserve">Server: </w:t></w:r><w:r><w:rPr><w:color w:val="008000" /></w:rPr><w:t xml:space="preserve">OK</w:t></w:r></w:p>
 <w:p xmlns:w="http://schemas.openxmlformats.org/wordprocessingml/2006/main"><w:r><w:t xml:space="preserve">● </w:t></w:r><w:r><w:t xml:space="preserve">Cache: </w:t></w:r><w:r><w:rPr><w:color w:val="FF0000" /></w:rPr><w:t xml:space="preserve">Down</w:t></w:r></w:p>
-<w:p xmlns:w="http://schemas.openxmlformats.org/wordprocessingml/2006/main"><w:r><w:t xml:space="preserve">Contact </w:t></w:r><w:r><w:rPr><w:u w:val="single" /><w:color w:val="0563C1" /></w:rPr><w:t xml:space="preserve">ops team</w:t></w:r><w:r><w:t xml:space="preserve"> (mailto:ops@example.com)</w:t></w:r><w:r><w:t xml:space="preserve"> for details.</w:t></w:r></w:p>
+<w:p xmlns:w="http://schemas.openxmlformats.org/wordprocessingml/2006/main"><w:r><w:t xml:space="preserve">Contact </w:t></w:r><w:r><w:rPr><w:color w:val="0563C1" /><w:u w:val="single" /></w:rPr><w:t xml:space="preserve">ops team</w:t></w:r><w:r><w:t xml:space="preserve"> (mailto:ops@example.com)</w:t></w:r><w:r><w:t xml:space="preserve"> for details.</w:t></w:r></w:p>

src/OpenXmlHtml.Tests/Samples/WordSamples.EmployeeOnboardingGuide.Net.verified.docx

@@ -2,4 +2,4 @@
 <w:p xmlns:w="http://schemas.openxmlformats.org/wordprocessingml/2006/main"><w:r><w:t xml:space="preserve">All systems </w:t></w:r><w:r><w:rPr><w:b /><w:color w:val="008000" /></w:rPr><w:t xml:space="preserve">operational</w:t></w:r><w:r><w:t xml:space="preserve">.</w:t></w:r></w:p>
 <w:p xmlns:w="http://schemas.openxmlformats.org/wordprocessingml/2006/main"><w:r><w:t xml:space="preserve">● </w:t></w:r><w:r><w:t xml:space="preserve">Server: </w:t></w:r><w:r><w:rPr><w:color w:val="008000" /></w:rPr><w:t xml:space="preserve">OK</w:t></w:r></w:p>
 <w:p xmlns:w="http://schemas.openxmlformats.org/wordprocessingml/2006/main"><w:r><w:t xml:space="preserve">● </w:t></w:r><w:r><w:t xml:space="preserve">Cache: </w:t></w:r><w:r><w:rPr><w:color w:val="FF0000" /></w:rPr><w:t xml:space="preserve">Down</w:t></w:r></w:p>
-<w:p xmlns:w="http://schemas.openxmlformats.org/wordprocessingml/2006/main"><w:r><w:t xml:space="preserve">Contact </w:t></w:r><w:r><w:rPr><w:u w:val="single" /><w:color w:val="0563C1" /></w:rPr><w:t xml:space="preserve">ops team</w:t></w:r><w:r><w:t xml:space="preserve"> (mailto:ops@example.com)</w:t></w:r><w:r><w:t xml:space="preserve"> for details.</w:t></w:r></w:p>
+<w:p xmlns:w="http://schemas.openxmlformats.org/wordprocessingml/2006/main"><w:r><w:t xml:space="preserve">Contact </w:t></w:r><w:r><w:rPr><w:color w:val="0563C1" /><w:u w:val="single" /></w:rPr><w:t xml:space="preserve">ops team</w:t></w:r><w:r><w:t xml:space="preserve"> (mailto:ops@example.com)</w:t></w:r><w:r><w:t xml:space="preserve"> for details.</w:t></w:r></w:p>

src/OpenXmlHtml.Tests/Samples/WordSamples.RichDocument.DotNet.verified.xml

@@ -1,3 +1,3 @@
-<w:p xmlns:w="http://schemas.openxmlformats.org/wordprocessingml/2006/main"><w:hyperlink w:anchor="section2"><w:r><w:rPr><w:u w:val="single" /><w:color w:val="0563C1" /></w:rPr><w:t xml:space="preserve">Jump to Section 2</w:t></w:r></w:hyperlink></w:p>
+<w:p xmlns:w="http://schemas.openxmlformats.org/wordprocessingml/2006/main"><w:hyperlink w:anchor="section2"><w:r><w:rPr><w:color w:val="0563C1" /><w:u w:val="single" /></w:rPr><w:t xml:space="preserve">Jump to Section 2</w:t></w:r></w:hyperlink></w:p>
 <w:p xmlns:w="http://schemas.openxmlformats.org/wordprocessingml/2006/main"><w:pPr><w:pStyle w:val="Heading2" /></w:pPr><w:bookmarkStart w:name="section2" w:id="1" /><w:r><w:rPr><w:b /></w:rPr><w:t xml:space="preserve">Section 2</w:t></w:r><w:bookmarkEnd w:id="1" /></w:p>
 <w:p xmlns:w="http://schemas.openxmlformats.org/wordprocessingml/2006/main"><w:r><w:t xml:space="preserve">Content here.</w:t></w:r></w:p>

src/OpenXmlHtml.Tests/Samples/WordSamples.RichDocument.Net.verified.xml

@@ -1,3 +1,3 @@
-<w:p xmlns:w="http://schemas.openxmlformats.org/wordprocessingml/2006/main"><w:hyperlink w:anchor="section2"><w:r><w:rPr><w:u w:val="single" /><w:color w:val="0563C1" /></w:rPr><w:t xml:space="preserve">Jump to Section 2</w:t></w:r></w:hyperlink></w:p>
+<w:p xmlns:w="http://schemas.openxmlformats.org/wordprocessingml/2006/main"><w:hyperlink w:anchor="section2"><w:r><w:rPr><w:color w:val="0563C1" /><w:u w:val="single" /></w:rPr><w:t xml:space="preserve">Jump to Section 2</w:t></w:r></w:hyperlink></w:p>
 <w:p xmlns:w="http://schemas.openxmlformats.org/wordprocessingml/2006/main"><w:pPr><w:pStyle w:val="Heading2" /></w:pPr><w:bookmarkStart w:name="section2" w:id="1" /><w:r><w:rPr><w:b /></w:rPr><w:t xml:space="preserve">Section 2</w:t></w:r><w:bookmarkEnd w:id="1" /></w:p>
 <w:p xmlns:w="http://schemas.openxmlformats.org/wordprocessingml/2006/main"><w:r><w:t xml:space="preserve">Content here.</w:t></w:r></w:p>

src/OpenXmlHtml.Tests/WordAnchorTests.BookmarksAndLinksDocx.DotNet.verified.docx

@@ -1 +1 @@
-<w:p xmlns:w="http://schemas.openxmlformats.org/wordprocessingml/2006/main"><w:r><w:t xml:space="preserve">Visit </w:t></w:r><w:r><w:rPr><w:u w:val="single" /><w:color w:val="0563C1" /></w:rPr><w:t xml:space="preserve">our site</w:t></w:r><w:r><w:t xml:space="preserve"> (https://example.com)</w:t></w:r><w:r><w:t xml:space="preserve"> for more info.</w:t></w:r></w:p>
+<w:p xmlns:w="http://schemas.openxmlformats.org/wordprocessingml/2006/main"><w:r><w:t xml:space="preserve">Visit </w:t></w:r><w:r><w:rPr><w:color w:val="0563C1" /><w:u w:val="single" /></w:rPr><w:t xml:space="preserve">our site</w:t></w:r><w:r><w:t xml:space="preserve"> (https://example.com)</w:t></w:r><w:r><w:t xml:space="preserve"> for more info.</w:t></w:r></w:p>