fix(ts-plugin): only inject Astro types into Astro projects

[lazerg]

Changes

• The TS plugin is registered globally, so it runs for every project in a workspace. Since Find Astro.locals references from .ts files in the TypeScript plugin #17269 it calls addAstroTypes() unconditionally, and findAstroPackageDirectory() just walks up the tree looking for node_modules/astro/. With a hoisted node_modules (pnpm nodeLinker: hoisted, npm, classic Yarn) that lookup succeeds from any sibling project, so env.d.ts and astro-jsx.d.ts were injected into projects that have nothing to do with Astro. Those files transitively pull in @types/node, and its global shims then win over lib.dom.d.ts, so "Go to Definition" on Blob, fetch or URL in a browser-only app lands in @types/node.
• Adds an isAstroProject() guard in front of the injection: the nearest package.json has to list astro, or there has to be an astro.config.* next to it. The language server already does this through getAstroInstall(), the plugin was the one place missing it.

Closes #17667

Testing

• Three cases in packages/language-tools/ts-plugin/test/units/astro-types.test.mts over a fixture monorepo with a hoisted node_modules: a React project that only reaches astro through the shared root is skipped, a project that depends on astro is detected, and so is one with an astro.config.mjs but no dependency.

Docs

• No docs change, this only narrows when the plugin injects its own ambient types.

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Latest commit: 7019410

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@astrojs/ts-plugin	Patch

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