fix(security): add SPA CSP, drop x-powered-by, strengthen dedupe hash

Address SonarQube security hotspots on the website:

- server/src/app.js: replace `contentSecurityPolicy: false` with a helmet CSP
  tuned for the built React SPA (script-src 'self'; style-src adds 'unsafe-inline'
  for React inline styles + the Google Fonts stylesheet; font-src gstatic; img-src
  allows data:/https: for uploads, embedded body images and BRAND_* assets;
  connect-src 'self' for REST+SSE). upgrade-insecure-requests is intentionally
  omitted (TLS terminates at the proxy; keeps local `npm start` over http working).
  The /api/docs Swagger UI route gets a scoped looser policy (inline script/style)
  since swagger-ui-express injects an inline bootstrap.
- client/vite.config.js: disable the inline module-preload polyfill so code-split
  builds keep `script-src 'self'` valid (RichTextEditor is a separate chunk).
- bot/src/app.js, server/src/internalApp.js: disable x-powered-by on the two
  internal-only listeners (the public app already strips it via helmet).
- shardEvents dedupe key: SHA-1 -> SHA-256 truncated to 40 hex chars (fits the
  existing CHAR(40) column, no migration; it is a content fingerprint, not a
  security value). schema.sql comment updated to match.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01NgyHnrNa8WwG3doxvxjuCr

server/src/app.js

@@ -36,11 +36,38 @@ app.use(trustProxyDebug)
 // obvious scanner probes are 404'd immediately without reaching real handlers.
 app.use(botScore.guard)
 
-// Security headers. CSP is left off here and will be tuned for the React SPA in
-// the frontend phase; the rest of helmet's protections stay enabled.
+// Security headers, including a Content-Security-Policy tuned for the built React
+// SPA. Notes on each non-'self' allowance:
+//   • style-src 'unsafe-inline' — React renders pervasive inline `style={{…}}`
+//     attributes, and CSP style *attributes* cannot be nonce'd; this is required.
+//     Also whitelists the Google Fonts stylesheet host.
+//   • font-src — Google Fonts (Cinzel) serves the font files from gstatic.
+//   • img-src https:/data: — uploaded images are same-origin, but wiki/news bodies
+//     (sanitizeHtml allows <img> over http/https) and BRAND_* logo/hero/favicon may
+//     point at external https images. http images are blocked by mixed-content on
+//     the https site anyway.
+//   • connect-src 'self' — the REST API and SSE streams are same-origin.
+//   • upgrade-insecure-requests is intentionally dropped: TLS is terminated at the
+//     proxy, there are no mixed-content subresources to upgrade, and leaving it on
+//     breaks a local `npm start` served over plain http.
+// The interactive API docs at /api/docs get their own looser policy below.
 app.use(
   helmet({
-    contentSecurityPolicy: false,
+    contentSecurityPolicy: {
+      useDefaults: true,
+      directives: {
+        'default-src': ["'self'"],
+        'script-src': ["'self'"],
+        'style-src': ["'self'", "'unsafe-inline'", 'https://fonts.googleapis.com'],
+        'font-src': ["'self'", 'https://fonts.gstatic.com'],
+        'img-src': ["'self'", 'data:', 'https:'],
+        'connect-src': ["'self'"],
+        'frame-ancestors': ["'self'"],
+        'object-src': ["'none'"],
+        'base-uri': ["'self'"],
+        'upgrade-insecure-requests': null,
+      },
+    },
     crossOriginResourcePolicy: { policy: 'cross-origin' },
   }),
 )
@@ -123,7 +150,18 @@ try {
     // #swagger.ignore = true
     res.json(swaggerSpec)
   })
-  app.use('/api/docs', swaggerUi.serve, swaggerUi.setup(swaggerSpec, {
+  // swagger-ui-express injects an inline bootstrap script and inline styles, which
+  // the global 'self'-only script-src would block — relax CSP for this route only.
+  const swaggerCsp = helmet.contentSecurityPolicy({
+    useDefaults: true,
+    directives: {
+      'script-src': ["'self'", "'unsafe-inline'"],
+      'style-src': ["'self'", "'unsafe-inline'"],
+      'img-src': ["'self'", 'data:', 'https:'],
+      'upgrade-insecure-requests': null,
+    },
+  })
+  app.use('/api/docs', swaggerCsp, swaggerUi.serve, swaggerUi.setup(swaggerSpec, {
     customSiteTitle: `${brand.name} API docs`,
     swaggerOptions: { persistAuthorization: true },
   }))