Use Effect schema JSON for mobile cache

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What Changed

• Decode and encode mobile shell snapshot cache documents with Schema.fromJsonString instead of manually parsing cache JSON before schema validation.
• Added focused mobile storage tests for valid cache loads, malformed JSON, unsupported schema versions, and environment mismatches.
• Updated shared Effect worker tests to use assert from @effect/vitest instead of Vitest expect.

Why

These are small idiomatic Effect cleanups that keep parsing/validation in Schema codecs and keep Effect tests aligned with the repo's @effect/vitest style.

UI Changes

Not applicable; no UI changes.

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

Verification:

• pnpm exec vp test run src/lib/storage.test.ts (from apps/mobile): 6 tests passed
• pnpm exec vp test run src/DrainableWorker.test.ts src/KeyedCoalescingWorker.test.ts (from packages/shared): 3 tests passed
• pnpm exec vp check: passed with 12 existing warnings
• pnpm exec vp run typecheck: passed

  

Note

Use Effect schema JSON codecs for mobile shell snapshot cache read/write

• Replaces manual JSON.parse/JSON.stringify + schema decode in storage.ts with Schema.fromJsonString-based codecs (CachedShellSnapshotJson, decodeCachedShellSnapshotJson, encodeCachedShellSnapshotJson).
• loadCachedShellSnapshot now decodes file contents directly via the schema codec, returning null on malformed JSON or schema mismatches instead of throwing.
• saveCachedShellSnapshot now passes { intermediates: true, overwrite: true } when creating the file, and skips writing if encoding yields None.
• Test suite in storage.test.ts adds in-memory mocks for expo-file-system and covers malformed JSON, unsupported schema versions, and mismatched environment IDs.
• Also migrates DrainableWorker and KeyedCoalescingWorker test assertions from expect to @effect/vitest assert.

^{Macroscope summarized 4966d41.}

[github-actions]

🚀 Expo continuous deployment is ready!

• Project → t3-code
• Platforms → android, ios
• Scheme → t3code-preview

	🤖 Android	🍎 iOS
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