Feat: Implement JWT bearer token authentication

Protects image upload, delete, and tag-update endpoints behind
Bearer token auth. Public read endpoints remain open. Angular SPA
gains a login page, auth interceptor, and route guard for /upload.

- JWTAuthProvider (HS256, sub/iat/exp, secrets.compare_digest)
- POST /api/v1/auth/token login endpoint
- require_auth FastAPI dependency on all write routes
- AuthService, LoginComponent, authInterceptor, authGuard
- Detail page hides write controls for unauthenticated visitors
- 43 unit tests passing; integration tests require Docker stack

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

api/app/config.py

@@ -1,4 +1,5 @@
 from functools import lru_cache
+
 from pydantic_settings import BaseSettings, SettingsConfigDict
 
 
@@ -13,6 +14,10 @@ class Settings(BaseSettings):
     s3_region: str = "us-east-1"
     api_base_url: str = "http://localhost:8000"
     max_upload_bytes: int = 52_428_800  # 50 MiB
+    jwt_secret_key: str
+    jwt_expiry_seconds: int = 86400
+    owner_username: str
+    owner_password: str
 
 
 @lru_cache