feat(files): play video and audio from outside the workspace too

A clip an agent wrote inside the workspace played with a working scrub bar,
while the same file in /tmp was refused as an unsupported type. The workspace
preview classified media with its own inline extension sets and the attachment
allowlist had no media at all, so the two paths disagreed about what a video is.

- VIDEO_ATTACHMENT_EXTENSIONS and AUDIO_ATTACHMENT_EXTENSIONS now live in
  attachment-registry.ts and are imported by file-content's classification, so
  both paths answer the same. mp4/webm/mov/m4v/ogv and
  mp3/wav/ogg/oga/m4a/aac/flac/opus join the attachment allowlist.
- Real MIME types for those extensions. Without one the raw route falls back to
  application/octet-stream, which a <video> refuses to decode: the player
  renders and then does nothing.
- getAttachmentType() gained the video and audio members of
  AttachmentDetectedType. Attachment cards have no per-type CSS and their
  thumbnail falls back to the type label, since the thumbnailer has no media
  branch and answers 204 rather than spawning a converter.
- The preview overlay's by-id branch renders <video>/<audio> with the same
  markup as the workspace branch, playsinline included. Serving was already
  range-aware, so seeking works.

The image-watcher keeps its own narrow detection list (png/pdf/docx/pptx), so
this does not start popping cards for every video an agent writes. Text types
that are not md or txt (.json, .log, code files) remain out of the allowlist by
choice and still report what is previewable instead.

Verified on an isolated instance: an external mp4 and mp3 both play, seek, and
report the right duration, matching the in-workspace clip exactly, and a click
on an external mp4 in the terminal opens the player with no attachment card.

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

test/routes/file-routes-attachment-path-guard.test.ts

@@ -357,6 +357,87 @@ describe('file-routes attachment path guard (COD-53)', () => {
     });
   });
 
+  // ===== Media (click-to-preview parity with the workspace preview) =====
+  // A video an agent writes inside the workspace plays with a working scrub
+  // bar; the same file in /tmp used to be refused as an unsupported type. Both
+  // now go through the same extension sets, and the raw route has to answer
+  // with a real media Content-Type and a range, or the player renders and then
+  // does nothing.
+  describe('media attachments', () => {
+    it('registers a video and serves it as seekable video/mp4', async () => {
+      const content = Buffer.from('MP4DATA-0123456789');
+      mockedStat.mockResolvedValue({ size: content.length, isFile: () => true, mtimeMs: 5 } as never);
+      mockedCreateReadStream.mockReturnValue(Readable.from([content.subarray(4, 10)]) as never);
+
+      const res = await harness.app.inject({
+        method: 'POST',
+        url: `/api/sessions/${harness.ctx._sessionId}/attachments`,
+        payload: { path: '/tmp/captures/demo.mp4', notify: false },
+      });
+      expect(res.statusCode).toBe(200);
+      const body = JSON.parse(res.body);
+      expect(body.data.attachmentType).toBe('video');
+
+      const rawRes = await harness.app.inject({
+        method: 'GET',
+        url: `/api/sessions/${harness.ctx._sessionId}/attachments/${body.data.attachmentId}/raw`,
+        headers: { range: 'bytes=4-9' },
+      });
+      expect(rawRes.statusCode).toBe(206);
+      expect(rawRes.headers['content-type']).toBe('video/mp4');
+      expect(rawRes.headers['content-range']).toBe(`bytes 4-9/${content.length}`);
+      expect(rawRes.headers['accept-ranges']).toBe('bytes');
+    });
+
+    it('registers audio with an audio type and its real MIME', async () => {
+      const content = Buffer.from('ID3AUDIO');
+      mockedStat.mockResolvedValue({ size: content.length, isFile: () => true, mtimeMs: 5 } as never);
+      mockedCreateReadStream.mockReturnValue(Readable.from([content]) as never);
+
+      const res = await harness.app.inject({
+        method: 'POST',
+        url: `/api/sessions/${harness.ctx._sessionId}/attachments`,
+        payload: { path: '/tmp/captures/take.mp3', notify: false },
+      });
+      expect(res.statusCode).toBe(200);
+      const body = JSON.parse(res.body);
+      expect(body.data.attachmentType).toBe('audio');
+
+      const rawRes = await harness.app.inject({
+        method: 'GET',
+        url: `/api/sessions/${harness.ctx._sessionId}/attachments/${body.data.attachmentId}/raw`,
+      });
+      expect(rawRes.statusCode).toBe(200);
+      expect(rawRes.headers['content-type']).toBe('audio/mpeg');
+    });
+
+    it('answers no thumbnail for media instead of spawning a converter', async () => {
+      // generateFirstPageThumbnail has no media branch; the card falls back to
+      // its type label. This pins that the route reports that cleanly.
+      const res = await harness.app.inject({
+        method: 'POST',
+        url: `/api/sessions/${harness.ctx._sessionId}/attachments`,
+        payload: { path: '/tmp/captures/clip.webm', notify: false },
+      });
+      const { attachmentId } = JSON.parse(res.body).data;
+
+      const thumbRes = await harness.app.inject({
+        method: 'GET',
+        url: `/api/sessions/${harness.ctx._sessionId}/attachments/${attachmentId}/thumbnail`,
+      });
+      expect(thumbRes.statusCode).toBe(204);
+    });
+
+    it('still refuses media in a blocked tree', async () => {
+      const res = await harness.app.inject({
+        method: 'POST',
+        url: `/api/sessions/${harness.ctx._sessionId}/attachments`,
+        payload: { path: '/root/private/recording.mp4', notify: false },
+      });
+      expect(res.statusCode).toBe(403);
+    });
+  });
+
   // ===== Quiet registration (click-to-preview) =====
   // The file-preview overlay registers a clicked out-of-workspace path to mint
   // an id it can render by. It is already putting the file on screen, so the