fix(matrix): isolate room context and restore reliable inbound dispatch (#18505)

* fix(matrix): isolate room context and inbound dispatch

* test(matrix): cover room isolation and dispatch regressions

* docs(matrix): document room isolation and session scope

* fix(matrix): stabilize CI requirement checks

* test(matrix): isolate mautrix stubs in requirements tests

* fix(matrix): port room-scoped status and resume to slash commands mixin

Move Matrix /status scope output and /resume same-room guards from the
pre-refactor gateway/run.py into gateway/slash_commands.py so PR #18505
foundation behavior survives the upstream god-file decomposition.

Uses i18n keys for Matrix resume/status messages. Preserves upstream
session.py fixes (role_authorized, DM user_id isolation).

* docs(matrix): explain inbound dispatch via handle_sync loop

Document why Hermes uses an explicit sync loop with handle_sync() rather than
client.start(), aligning with upstream #7914 diagnostics while preserving
Hermes background maintenance tasks.

* fix(i18n): add Matrix resume/status keys to all locale catalogs

The Matrix /resume and /status slash-command keys added in the foundation
PR must exist in every supported locale file. tests/agent/test_i18n.py
asserts key and placeholder parity across catalogs.

Non-English locales use English strings as interim placeholders until
community translators can localize them.

* fix(matrix): restore gateway authz for allowed_users; honor config require_mention

Revert the early MATRIX_ALLOWED_USERS gate in _on_room_message so inbound
sender authorization stays in gateway authz like main. Parse require_mention
from config.extra (platforms.matrix / top-level matrix yaml) with env fallback,
matching thread_require_mention and fixing Forge when require_mention is set
only in profile config.yaml.

* fix(matrix): harden status scope and allowlisted DMs

* fix(matrix): use session store lookup for resume scope

tests/gateway/test_matrix_exec_approval.py

@@ -27,9 +27,9 @@ class TestMatrixExecApprovalReactions:
         assert result.success is True
         assert adapter._approval_prompt_by_session["sess-1"] == "$evt1"
         assert adapter._approval_prompts_by_event["$evt1"].session_key == "sess-1"
-        assert adapter._send_reaction.await_count == 2
+        assert adapter._send_reaction.await_count == 3
         emojis = [call.args[2] for call in adapter._send_reaction.await_args_list]
-        assert emojis == ["✅", "❎"]
+        assert emojis == ["✅", "♾️", "❌"]
 
     @pytest.mark.asyncio
     async def test_reaction_resolves_pending_approval(self, monkeypatch):