HTTP transport: drop WS server, offline send queue + dead-stream watchdog

Gateway (docs/19):
- Remove ws_server.py; frame dispatch factored into dispatch.py
- http_server: media upload/pull, pairing over HTTP
- protocol: media frames mirrored; tests + ws_probe updated for HTTP

App:
- HttpGateway: postFrame/uploadMedia/pullMedia no longer throw on
  network failure (PostResult ok=false / Result.failure) — uncaught
  SocketTimeoutException on Dispatchers.Default crashed the app
- GatewayClient: dead-stream watchdog (health probe every 10s, 2
  failures -> redial in ~20s instead of the 45s SSE read timeout);
  state flips to Reconnecting when the stream dies, restored from the
  last hello.ack on long-poll success; poke() + backoff reset on app
  resume (MainActivity.onResume)
- Offline sends: composer enabled while disconnected; a send with no
  response (status 0) stays queued (Pending) and is auto-resent on the
  next (re)connect after a 2s outbox-replay grace; gateway 4xx
  rejections fail the bubble (tap to retry, no auto-loop)
- ChatStore: echo-replace and thread-relocate also match Failed
  bubbles (POST response lost in a network drop); loadHistory dedupes
  local failed bubbles the server already has; failMessage()
- MainActivity: poke() on resume so a backgrounded app reconnects
  promptly instead of waiting out the backoff

gateway-plugin/pairing.py

@@ -45,7 +45,7 @@ def verify_token(provided: str | None, expected: str | None) -> bool:
 def qr_payload(host: str, port: int, token: str, secure: bool = False) -> str:
     """Pairing URL encoded into the QR / pre-filled into the app.
 
-    ``iris://pair?host=<lan-ip>&port=8790&token=<token>`` — the app's
+    ``iris://pair?host=<lan-ip>&port=8791&token=<token>`` — the app's
     Connect screen parses this to pre-fill settings (docs/09 §9.2).
     """
     return (
@@ -57,9 +57,9 @@ def qr_payload(host: str, port: int, token: str, secure: bool = False) -> str:
 
 
 def pairing_url(host: str, port: int, secure: bool = False) -> str:
-    """Plain ws(s) URL the app connects to (shown next to the QR)."""
-    scheme = "wss" if secure else "ws"
-    return f"{scheme}://{host}:{int(port)}/ws"
+    """Plain http(s) URL the app connects to (shown next to the QR)."""
+    scheme = "https" if secure else "http"
+    return f"{scheme}://{host}:{int(port)}"
 
 
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