feat(web): gesture-control overlay integration (Phase 5, opt-in via CODEMAN_GESTURE=1)

Loads a hand-tracking overlay into the dashboard that detaches a session by
pinch-grabbing its tab and pulling it out — driving the existing
app.detachSession(id) hook. Bundle (src/web/public/gesture/gesture-codeman.js)
is built from the codeman-gesture-control project's src/codeman/entry.ts
(esbuild, MediaPipe included) and served same-origin.

OFF by default — guarded entirely by CODEMAN_GESTURE=1:
- server.ts: injects the module script into the dashboard HTML only (not solo
  /session/:id popups, which have no tab strip).
- auth.ts: widens CSP only under the flag — adds 'wasm-unsafe-eval' (MediaPipe
  WASM) and the pinned MediaPipe CDNs (cdn.jsdelivr.net wasm, storage.googleapis.com
  model) to connect-src, plus worker-src 'self' blob:. Production CSP is unchanged
  when the flag is off.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/web/server.ts

@@ -1007,6 +1007,13 @@ export class WebServer extends EventEmitter {
       const safeId = JSON.stringify(soloSessionId).replace(/</g, '\\u003c');
       html = html.replace('</head>', `<script>window.__CODEMAN_SOLO__=${safeId};</script>\n</head>`);
     }
+    // Gesture-control overlay (Phase 5): dashboard only (not solo popups, which
+    // have no tab strip), opt-in via CODEMAN_GESTURE=1. The bundle is served
+    // same-origin from /gesture/ so 'self' covers it; CSP is widened to match in
+    // registerSecurityHeaders under the same flag.
+    if (!soloSessionId && process.env.CODEMAN_GESTURE === '1') {
+      html = html.replace('</head>', `<script type="module" src="/gesture/gesture-codeman.js"></script>\n</head>`);
+    }
     return html;
   }