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/media.py

@@ -20,7 +20,6 @@ live under ``get_hermes_home()/"android"/media/tmp``.
 Milestone M4.
 """
 
-import asyncio
 import contextlib
 import hashlib
 import logging
@@ -434,27 +433,3 @@ class MediaStore:
             for k in stale:
                 del self._outbound[k]
         return len(stale)
-
-
-async def stream_file(
-    ws, path: str, chunk_bytes: int = DEFAULT_CHUNK_BYTES, timeout: float = 10.0
-) -> int:
-    """Stream *path* to *ws* as binary frames. Returns bytes sent.
-
-    Ordering is guaranteed by the WebSocket; the caller sends the terminal
-    ``media.pull.end`` frame afterwards. Each chunk send is bounded by
-    *timeout* so a stalled puller can't wedge the handler forever (the
-    caller treats the raised error as an aborted pull).
-    """
-    sent = 0
-    # Safe: ``path`` is produced by hermes ``cache_*_from_bytes`` (a path inside
-    # hermes's own media cache dir), never derived from raw user input.
-    # pi-lens-ignore: python-path-traversal
-    with open(path, "rb") as f:
-        while True:
-            chunk = f.read(chunk_bytes)
-            if not chunk:
-                break
-            await asyncio.wait_for(ws.send(chunk), timeout=timeout)
-            sent += len(chunk)
-    return sent