Quiet optimized dependency sourcemap warnings

[lukemelia]

Summary

• Adds a serve-only Vite middleware that pads optimized dependency sourcemaps before Vite transforms the matching optimized dep JavaScript file.
• Prevents Vite from hydrating missing sourcesContent entries from pnpm package paths outside packages/host/node_modules/.vite, which removes the repeated "Sourcemap for ... points to a source file outside its package" warnings.

Validation

• Reproduced the warning with pnpm start in packages/host before the change.
• Verified optimized dependency requests no longer print the sourcemap warning after the change.
• Confirmed affected maps are padded so sourcesContent length matches sources length.
• Ran mise exec -- pnpm lint in packages/host.
• Ran mise exec -- pnpm build in packages/host.

[github-actions]

Preview deployments

• Host staging preview

• Host production preview

Host Test Results

    1 files  ±    0      1 suites  ±0   1h 44m 12s ⏱️ - 3h 29m 39s
2 565 tests +    3  2 550 ✅ +   10  15 💤 ± 0  0 ❌ ± 0 
2 584 runs   - 5 159  2 569 ✅  - 5 101  15 💤  - 30  0 ❌  - 14 

Results for commit 0bf39eb. ± Comparison against earlier commit dffbbca.

Realm Server Test Results

    1 files  ± 0      1 suites  ±0   18m 29s ⏱️ +11s
1 239 tests +21  1 239 ✅ +21  0 💤 ±0  0 ❌ ±0 
1 317 runs  +27  1 317 ✅ +27  0 💤 ±0  0 ❌ ±0 

Results for commit 0bf39eb. ± Comparison against earlier commit dffbbca.

[Copilot]

Pull request overview

This PR adds a Vite dev-server middleware in packages/host to patch optimized dependency sourcemaps on the fly so Vite stops emitting repeated sourcemap warnings during pnpm start.

Changes:

• Adds a serve-only Vite plugin that intercepts optimized dependency requests under node_modules/.vite/deps.
• Reads matching .js.map files and pads missing sourcesContent entries before Vite continues serving the dependency.
• Wires the new middleware into the host app’s Vite plugin list.

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