fix: improve project favicon detection for monorepos

[ponbac]

What Changed

Improve project favicon detection without introducing a broad recursive search.
Closes #1020.

Rules, in order:

• Check well-known favicon paths in the requested project root.
  Example: /repo/favicon.svg or /repo/public/favicon.ico.
• If none exist, look for <link rel="icon" ... href="..."> tags or object-style { href, rel: "icon" } declarations in a small set of common source files, then resolve that target.
  Example: /repo/index.html points to /brand/logo.svg, so the route first tries /repo/public/brand/logo.svg and then /repo/brand/logo.svg.
• If still nothing is found, repeat the same checks for first-level children of apps/ and packages/, plus other top-level directories in the requested root, using the same non-git directory ignore rules as workspaceEntries.
  Example: /repo/apps/web/public/favicon.png or /repo/frontend/public/favicon.png is found when the cwd is /repo.
• Prefer a root match over nested workspace matches.
  Example: /repo/favicon.svg wins over /repo/apps/web/public/favicon.ico.
• Fall back to the existing generated SVG when nothing is found.

I also extracted the shared gitignore probing into apps/server/src/gitIgnore.ts so both workspaceEntries and projectFaviconRoute use the same chunked git check-ignore --no-index -z --stdin filtering. I also extracted the shared workspace directory ignore policy into apps/server/src/workspaceIgnore.ts, so projectFaviconRoute now uses the same non-git skip rules as workspaceEntries when scanning nested roots instead of keeping a separate ignore list.

Why

The current behavior misses common monorepo layouts where the favicon lives under an app directory instead of the repo root.

There was already an earlier PR for this in the upstream repo: #690. That version was larger and messier. This keeps the rules simple on purpose, leaving more extensive changes to project icons for trusted maintainers.

UI Changes

Not applicable.

Checklist

• This PR is small and focused
• I explained what changed and why
• I included before/after screenshots for any UI changes
• I included a video for animation/interaction changes

Note

Fix project favicon detection to support monorepo layouts with gitignore awareness

• Refactors tryHandleProjectFaviconRequest in projectFaviconRoute.ts to run as an Effect with a FileSystem service, replacing the previous synchronous handler.
• Adds gitignore-aware path filtering via a new gitIgnore.ts module that uses git check-ignore --stdin batching to skip ignored candidates.
• Searches monorepo roots (apps/, packages/, top-level dirs) and source files (index.html, src/root.tsx, app/root.tsx) to resolve favicons in nested apps, preferring the project root favicon first.
• Extracts shared workspace ignore logic into workspaceIgnore.ts and updates workspaceEntries.ts to import from the new modules.

^{Macroscope summarized c396c88.}

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