Rooms are served by a build without WebSocket

[EdmondDantes]

The room core stopped knowing what a connection is three PRs ago. The build gate
still said otherwise: src/room/*.c sat behind --enable-websocket, the Room
class was guarded, and each of the six HttpServer room methods carried an
#else arm that threw "Rooms require the extension built with WebSocket
support". A build configured with --disable-websocket now compiles the core,
registers Room, and delivers a publish from one thread to a recv() in
another.

The BC break

RoomDeliveryException moves to stubs/RoomExceptions.php and extends
HttpServerException instead of WebSocketException — rooms are served where
WebSocketException does not exist. A handler that caught WebSocketException
around Room::send() / HttpServer::send() no longer catches it. CHANGELOG.md
carries it under Unreleased, and test 059, which asserted the old chain, asserts
the new one.

Nothing else about the exception changed: same delivered / pending counts,
same message, same distinctness from WebSocketBackpressureException.

Two defects only this configuration could show

Both were found by building it, and both are fixed here:

• getRuntimeStats() reported no room counters. The whole block sat behind
  the WebSocket guard, though the counters belong to the core. Every build
  reports them now; the ws_* key names stay, because php-claw and the tests
  read them.
• room_hub_thread_sweep() sat behind the guard too. A thread that
  subscribed to a room has no other detach, so without WebSocket it never
  detached: a leaked mailbox and a live libuv handle at request shutdown
  (uv_loop_close failed (EBUSY)).

The gate

A step on the debug leg builds --disable-websocket in a copy of the tree and
runs tests/phpt/room. Review found the first version of it broken in three
ways, all fixed:

• It probed with -d extension=<abs path> while the runner's scan dir already
  loads the same module by name from the WebSocket build. PHP keeps the first
  load and discards the second, so the probe saw TrueAsync\WebSocket and failed
  on every run. Reproduced locally with a scan-dir ini, and -d extension_dir
  fixes it — measured both ways.
• It configured only --enable-http-server, so it built an HTTP/1-only,
  TLS-less extension: it answered "do the room sources link" rather than "does
  the product build". It now takes the same flags as the real build, minus
  WebSocket.
• It ran one test that is allowed to skip, and run-tests exits 0 when
  everything skips. The ten connectionless room tests move from
  tests/phpt/websocket/ to tests/phpt/room/, the leak lane follows them, and
  the step now asserts that at least ten tests actually passed.

Measured

• WebSocket build: tests/phpt 382 passed, 0 failed, 1 warned (an XFAIL section
  on a passing test, pre-existing). tests/valgrind-rooms.sh 10 tests, 0 leaked.
• --disable-websocket build: no warnings of ours, nm -u shows no undefined
  symbol of ours, the extension loads, TrueAsync\Room and
  TrueAsync\RoomDeliveryException exist with WebSocket absent, and all 11
  tests in tests/phpt/room pass.

Corrected on the way

The "Rooms are not available" message told the caller to use
addWebSocketHandler(), which never allocated the hub in either build; the same
false claim was in stubs/HttpServer.php. Also fixed: a runtime message about
"the WebSocket topic hub", the Room stub describing a subscriber as a WebSocket
connection, docs/PLAN_RELIABLE_ROOM_PUBLISH.md on the exception's parent, and
three file comments that asserted the opposite of what the code now does.

[github-actions]

Coverage

Total lines: 82.24% → 82.33% (+0.09 pp)

File	Baseline	Current	Δ	Touched
src/core/http_connection.c	75.26%	75.55%	+0.29 pp
src/http3/http3_callbacks.c	82.98%	83.09%	+0.11 pp
src/http3/http3_io.c	89.09%	89.45%	+0.36 pp
src/http3/http3_listener.c	76.88%	78.53%	+1.65 pp
src/http3/http3_packet.c	85.22%	90.43%	+5.22 pp
src/http_server.c	95.20%	95.20%	+0.00 pp	●
src/http_server_class.c	75.07%	75.03%	-0.04 pp	●
src/room/php_room.c	82.37%	82.46%	+0.09 pp	●
src/websocket/php_websocket.c	78.68%	78.61%	-0.07 pp	●
src/websocket/ws_session.c	90.41%	90.59%	+0.18 pp