fix(files): open file paths agents print, from the terminal and the chat

A path an agent prints was already underlined in the terminal, but clicking
one opened the preview overlay on "File not found": file-content/file-raw
resolve against the session workingDir and refuse anything outside it, and the
paths agents print most (a /tmp capture, Claude's own scratchpad, another
checkout) are outside it by definition. In the response viewer those paths were
not links at all.

- openFilePreview() detects an out-of-workspace path and registers it through
  POST /api/sessions/:id/attachments first, rendering by attachment id. That is
  the surface built for live external files, so the server-side guard is
  unchanged: secret trees blocked, symlinks resolved, extension allowlist. The
  workspace routes keep refusing escapes exactly as before.
- New optional `notify` field on that route. `notify: false` suppresses only the
  attachment:detected broadcast, so a click does not also pop a card announcing
  the file already filling the screen. Default stays true for the CLI and
  publish callers.
- _linkifyFilePaths() links paths in rendered response-viewer markdown. It walks
  text nodes and builds anchors with DOM APIs (the source is model output; never
  a string rebuild of sanitized markup), skips subtrees already inside an <a>,
  and keeps the message text byte-identical so copy-code is unaffected.
- One path pattern in constants.js now feeds both the xterm link provider and
  the chat linkifier, a fresh instance per call since lastIndex is per-object
  state. It picks up /Users and /mnt roots (nothing was clickable on macOS or
  WSL), plus docx/pptx and video/audio extensions.
- .file-preview-overlay moves to z-index 5100, above the response viewer at
  5000. At its old 2000 a path clicked in the chat opened the overlay behind the
  panel it was launched from.

Verified end to end on an isolated instance, desktop and phone viewport: real
clicks in the terminal and the chat both render the image, external md and pdf
render, /etc/hosts is still refused, workspace previews unchanged.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

src/web/routes/file-routes.ts

@@ -1449,7 +1449,7 @@ export function registerFileRoutes(app: FastifyInstance, ctx: SessionPort & Even
   app.post('/api/sessions/:id/attachments', async (req, reply) => {
     const { id } = req.params as { id: string };
     const session = findSessionOrFail(ctx, id, req);
-    const body = (req.body || {}) as { path?: string };
+    const body = (req.body || {}) as { path?: string; notify?: boolean };
 
     if (!body.path || typeof body.path !== 'string') {
       reply.code(400).send(createErrorResponse(ApiErrorCode.INVALID_INPUT, 'Missing attachment path'));
@@ -1458,7 +1458,15 @@ export function registerFileRoutes(app: FastifyInstance, ctx: SessionPort & Even
 
     try {
       const event = await registerExternalAttachment(id, body.path, { sessionWorkingDir: session.workingDir });
-      ctx.broadcast(SseEvent.AttachmentDetected, event);
+      // `notify: false` registers QUIETLY. The file-preview overlay uses it to
+      // mint an id for a path the user just clicked (a terminal or response-viewer
+      // link pointing outside the workspace): it is already opening the file, so
+      // the attachment card + unread badge would be noise announcing what is
+      // filling the screen. Default stays true — every other caller (the
+      // `codeman attach` CLI, codeman-publish) wants the card.
+      if (body.notify !== false) {
+        ctx.broadcast(SseEvent.AttachmentDetected, event);
+      }
       return { success: true, data: event };
     } catch (err) {
       if (err instanceof AttachmentRegistrationError) {