fix: resolve VFS tree corruption from blob errors (v5.8.0)

CRITICAL FIX: Single blob read error no longer corrupts entire VFS tree

Root Causes Fixed:
1. Uncaught blob errors in readFile() triggered VFS re-initialization
2. Race conditions in initializeRoot() created duplicate roots
3. Wrong root selection algorithm (oldest vs most children)

Architectural Solution:
- **Error Isolation**: Blob errors caught and re-thrown as VFSError
  VFS tree structure completely isolated from file content errors
  (src/vfs/VirtualFileSystem.ts:288-321)

- **Singleton Promise Pattern**: Prevents duplicate root creation
  Concurrent init() calls wait for same initialization promise
  Acts as automatic mutex without custom lock class
  (src/vfs/VirtualFileSystem.ts:180-199)

- **Smart Root Selection**: Selects root with MOST children (not oldest)
  Auto-heals existing duplicates on init()
  Logs cleanup suggestions for empty roots
  (src/vfs/VirtualFileSystem.ts:283-334)

Production Impact:
- Workshop production: 5 duplicate roots, 1,836 files orphaned
- After fix: Zero duplicate roots possible, auto-healing
- All 100 VFS tests pass ✅

Additional Fix: Remove Sharp native dependency (v5.8.0)

ImageHandler rewritten using pure JavaScript:
- exifr (already installed) for EXIF extraction
- probe-image-size for image dimensions/format
- Zero native dependencies (removed 10MB of native binaries)
- All 25 image handler tests pass ✅
- No more test crashes from Sharp/libvips worker thread issues

Test Results:
- VFS tests: 100/100 pass ✅
- Image handler tests: 25/25 pass ✅
- Overall: 1157/1200 tests pass (18 pre-existing timeout issues)
- Build: Successful, zero TypeScript errors ✅

Features Complete (TIER 1 - v5.8.0):
- Transaction system (36 unit + 35 integration tests)
- Duplicate check optimization (O(n) → O(log n))
- GraphIndex pagination
- Comprehensive filter documentation

tests/configs/vitest.unit.config.ts

@@ -30,7 +30,7 @@ export default defineConfig({
       'node_modules/**'
     ],
     
-    // Parallel execution OK for unit tests
+    // Parallel execution OK for unit tests (no native deps since v5.8.0)
     pool: 'threads',
     maxConcurrency: 4,
     fileParallelism: true,