Finish Phase 6: Push frontend, WebAuthn frontend, OpenAPI/Swagger

Frontend:
- stores/push.ts: fixed VAPID key endpoint, added checkSubscription, proper subscription format
- UserSettings.tsx: added [ENABLE PUSH] toggle and [REGISTER PASSKEY] button
- LoginForm.tsx: added [SIGN IN WITH PASSKEY] button

Backend:
- cmd/server/main.go: added Swagger annotations, /docs/* route
- docs/: generated swagger.json, swagger.yaml, docs.go
- Makefile: added docs target for swag init

web/src/components/LoginForm.tsx

@@ -85,6 +85,42 @@ export function LoginForm() {
             {isLoading ? '[PROCESSING...]' : isRegister ? '[REGISTER]' : '[LOGIN]'}
           </button>
         </form>
+        {!isRegister && (
+          <div className="mt-3">
+            <button
+              type="button"
+              onClick={async () => {
+                try {
+                  // Get challenge from server
+                  const resp = await fetch('/api/v1/auth/webauthn/login/begin', { method: 'POST', credentials: 'include' });
+                  if (!resp.ok) throw new Error('Passkey login not available');
+                  const options = await resp.json();
+                  
+                  // Use WebAuthn API
+                  const credential = await navigator.credentials.get({ publicKey: options });
+                  if (!credential) return;
+                  
+                  // Send to server
+                  const finishResp = await fetch('/api/v1/auth/webauthn/login/finish', {
+                    method: 'POST',
+                    credentials: 'include',
+                    headers: { 'Content-Type': 'application/json' },
+                    body: JSON.stringify(credential),
+                  });
+                  
+                  if (finishResp.ok) {
+                    navigate('/');
+                  }
+                } catch (err) {
+                  console.error('Passkey login failed:', err);
+                }
+              }}
+              className="terminal-button w-full border-gb-aqua text-gb-aqua"
+            >
+              [SIGN IN WITH PASSKEY]
+            </button>
+          </div>
+        )}
         <div className="mt-4 text-center">
           <button
             type="button"