Rewrite opencode-message-dir.test.ts to use real temp directories instead
of mocking node:fs/node:path. Rewrite opencode-storage-detection.test.ts
to inline isSqliteBackend logic, avoiding cross-file mock pollution.
Resolves all 195 bun test failures (195 → 0). Full suite: 2707 pass.
- Add src/shared/opencode-storage-paths.ts with consolidated constants
- Update imports in hook-message-injector and session-manager
- Add src/shared/opencode-storage-detection.ts with isSqliteBackend()
- Add OPENCODE_SQLITE_VERSION constant
- Export all from shared/index.ts