feat: add HTMX web UI with login/register forms

- Home page showing README and stats
- Login/register forms with HTMX
- Registry and activities pages
- Cookie-based auth for web UI
- JWT secret from Docker secrets (/run/secrets/jwt_secret)
- Updated README with secret generation instructions

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

auth.py

@@ -20,11 +20,29 @@ from pydantic import BaseModel
 pwd_context = CryptContext(schemes=["bcrypt"], deprecated="auto")
 
 # JWT settings
-SECRET_KEY = os.environ.get("JWT_SECRET", secrets.token_hex(32))
 ALGORITHM = "HS256"
 ACCESS_TOKEN_EXPIRE_DAYS = 30
 
 
+def load_jwt_secret() -> str:
+    """Load JWT secret from Docker secret, env var, or generate."""
+    # Try Docker secret first
+    secret_path = Path("/run/secrets/jwt_secret")
+    if secret_path.exists():
+        return secret_path.read_text().strip()
+
+    # Try environment variable
+    if os.environ.get("JWT_SECRET"):
+        return os.environ["JWT_SECRET"]
+
+    # Generate one (tokens won't persist across restarts!)
+    print("WARNING: No JWT_SECRET configured. Tokens will be invalidated on restart.")
+    return secrets.token_hex(32)
+
+
+SECRET_KEY = load_jwt_secret()
+
+
 class User(BaseModel):
     """A registered user."""
     username: str