feat(mobile): phone Attach button and camera-roll video uploads

A phone-only toolbar Attach button hands the agent a photo or a video with the
keyboard down. It owns its own file input, positioned over the button so iOS
anchors the picker popover to it; the picked paths land on the prompt as unsent
text, so Compose adopts them together with anything already typed and Use
terminal keyboard hands a single-line draft back the other way.

Videos take a second path on the same route: ?kind=video streams the file to
disk under MAX_PASTE_VIDEO_BYTES (1GB, env CODEMAN_MAX_PASTE_VIDEO_BYTES)
instead of buffering it, sniffs the container from the first bytes as they
arrive, drains a mislabeled body unwritten and unlinks on any failure. It draws
on its own 3/min per-(IP, session) rate bucket beside the image path's 30/min:
at 1GB each, 30/min would be 30GB of disk a minute. Without the flag the route
is byte-identical to the image-only version, same 50MB cap and same bucket.

One client classifier, _promptAttachKind (MIME first, then the name's
extension), drives every pick and paste surface: the Attach button, terminal
drop, the tile grid's drop, the Compose and paste-dialog pickers and the
clipboard handlers. A pick that lands while the tile grid owns the terminal
goes to the PTY rather than the parked main-terminal overlay.

src/config/buffer-limits.ts

@@ -113,6 +113,16 @@ export const FILE_PEEK_BYTES = 8 * 1024 - 1; // 8KB (inclusive end offset)
  */
 export const MAX_PASTE_IMAGE_BYTES = parseInt(process.env.CODEMAN_MAX_PASTE_IMAGE_BYTES || '') || 50 * 1024 * 1024; // 50MB
 
+/**
+ * Maximum size (bytes) of a single video uploaded via POST
+ * /api/sessions/:id/paste-image?kind=video (the phone toolbar's Attach button
+ * offers the camera roll's videos beside its photos). Videos stream to disk
+ * rather than through memory, so this is a disk-fill sanity bound, not a memory
+ * bound: a minute of 4K60 from an iPhone is about 400MB, so the image cap would
+ * refuse most clips. Override: CODEMAN_MAX_PASTE_VIDEO_BYTES (bytes)
+ */
+export const MAX_PASTE_VIDEO_BYTES = parseInt(process.env.CODEMAN_MAX_PASTE_VIDEO_BYTES || '') || 1024 * 1024 * 1024; // 1GB
+
 // ============================================================================
 // File Download Limits
 // ============================================================================