Add QR pairing (terminal QR, in-app scanner, iris://pair deep link)

docs/protocol/frames.schema.json

@@ -10,7 +10,7 @@
       "v": { "type": "integer", "const": 1, "description": "Protocol version." },
       "id": { "type": "integer", "description": "Request id; present on requests and their responses/acks. Absent on pure events." },
       "type": { "type": "string", "description": "Frame type (see frame_types)." },
-      "chat_id": { "type": "string", "description": "Optional chat scope (e.g. android:default, android:chan_7)." },
+      "chat_id": { "type": "string", "description": "Optional chat scope (e.g. default, chan_7)." },
       "thread_id": { "type": "string", "description": "Optional thread scope within a chat_id." },
       "cursor": { "type": "integer", "description": "Outbox cursor the frame was parked under. Present ONLY on frames replayed by sync (live frames carry none). The app skips re-notifying replayed frames with cursor <= last_pushed_cursor (docs/08 §8.7)." },
       "payload": { "type": "object", "description": "Type-specific payload." }