feat(file-preview): render local HTML files as sandboxed pages

Clicking an agent's `.html` path showed source text or downloaded it, so a
generated report could only be viewed by asking the agent to start a web
server. Render it instead, without serving HTML same-origin:

- POST /api/sessions/:id/html-view mints a capability for the file's own
  directory (workspace path, or outside it under the attachment guard).
- GET /html-view/:cap/* serves the page and its relative assets with
  `Content-Security-Policy: sandbox` WITHOUT allow-same-origin, so the page
  runs in an opaque origin (also as a top-level tab) and cannot read the
  Codeman document, its cookies or its API.
- Served files: non-dot, asset-allowlisted, realpath-confined to that
  directory, blocklist applied; GET only. Capabilities are memory-only with a
  rolling TTL and are revoked with the web-tab ones on logout.
- Frontend: the file preview renders HTML in a sandboxed iframe (popout opens
  the same URL); terminal `.html` links go to the preview, not the log viewer.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

src/web/server.ts

@@ -178,6 +178,7 @@ import {
   registerTeamRoutes,
   registerMuxRoutes,
   registerFileRoutes,
+  registerHtmlViewRoutes,
   registerScheduledRoutes,
   registerHookEventRoutes,
   registerApprovalRoutes,
@@ -1116,6 +1117,7 @@ export class WebServer extends EventEmitter {
     registerTeamRoutes(this.app, ctx);
     registerMuxRoutes(this.app, ctx);
     registerFileRoutes(this.app, ctx);
+    registerHtmlViewRoutes(this.app, ctx);
     registerScheduledRoutes(this.app, ctx);
     registerHookEventRoutes(this.app, ctx);
     registerApprovalRoutes(this.app, ctx);