feat: directory scanner plugin — walk library paths, auto-register assets

- DirectoryScannerPlugin: recursive directory walk via FileStoragePort
- Computes SHA256 checksums, classifies media by extension
- Registers each file via RegisterAssetHandler (triggers AssetIngested → extract_metadata pipeline)
- Reads library_path_id from job payload, looks up volume + path
- Seeded plugin + scan_directory pipeline
- Trigger via POST /jobs with { job_type: "ScanDirectory", payload: { library_path_id: "..." } }

k-photos-frontend/.gitignore

@@ -0,0 +1,36 @@
+# dependencies
+/node_modules
+/.pnp
+.pnp.*
+.yarn/*
+!.yarn/patches
+!.yarn/plugins
+!.yarn/releases
+!.yarn/versions
+
+# testing
+/coverage
+
+# next.js
+/.next/
+/out/
+
+# production
+/build
+
+# misc
+.DS_Store
+*.pem
+
+# debug
+npm-debug.log*
+yarn-debug.log*
+yarn-error.log*
+pnpm-debug.log*
+
+# env files (can opt-in for committing if needed)
+.env*
+
+# typescript
+*.tsbuildinfo
+next-env.d.ts