fix: simplify SDK catalog defaults

[Jiayi-Ye02]

Summary

• Remove the product and platform filter controls from the Chinese SDK catalog.
• Keep existing product/platform URL filtering compatibility for embedded and historical links.
• Collapse every SDK product by default while preserving the capability-group table of contents.

Follow-up

• Follow-up to feat: improve Chinese SDK download catalog #1064.

Verification

• Focused SDK and navigation tests: 42 passed.
• TypeScript check: passed.
• Biome check: passed.
• Browser preview at 1440x900: no catalog filter controls, zero products expanded by default, capability-group TOC present, page-level horizontal overflow is 0.

Known baseline failures

• The full test suite has 35 pre-existing failures in unrelated route, DocsShell, generated-content, and FAQ fixture tests. This follow-up PR is intentionally opened with those known baseline failures, as authorized in the task conversation.

[github-actions]

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