feat(gui): first-class Messaging page + gateway menu redesign

- Add Messaging page to the desktop app with per-platform setup,
  status, and inline guidance. Catalog derives from gateway.config
  Platform enum + plugin registry, so every messaging adapter the CLI
  supports (Telegram, Discord, Slack, Mattermost, Matrix, WhatsApp,
  Signal, BlueBubbles, Home Assistant, Email, SMS, DingTalk, Feishu,
  WeCom, Weixin, QQ, Yuanbao, API server, Webhooks, plugins) shows up
  without per-platform code.
- New REST endpoints: GET /api/messaging/platforms, PUT and POST
  /test on the same path. Secrets go through the existing .env
  pipeline; enable/disable writes config.yaml.
- Replace gateway statusbar dropdown with a richer panel: status row,
  icon-only restart + system-panel actions, recent activity (with
  timestamps trimmed in display, full text on hover), platform list.
- Auto-poll the messaging page every 6s (paused when hidden) so
  status updates without a manual check.
- Drop Settings / Command Center from the sidebar nav (still
  reachable via shortcuts and the titlebar cog).
- Flatten top corners on Messaging/Skills/Artifacts/Chat panes.
- Share new StatusDot component across messaging + gateway menu.
- Fix gateway/config.py so an explicit platforms.<name>.enabled=false
  in config.yaml is honored when env tokens are present.
- pb-9 on the chat content area for breathing room above the composer.

tests/hermes_cli/test_web_server.py

@@ -345,6 +345,82 @@ class TestWebServerEndpoints:
 
         assert resp.status_code == 200
 
+    def test_get_messaging_platforms(self):
+        resp = self.client.get("/api/messaging/platforms")
+
+        assert resp.status_code == 200
+        platforms = resp.json()["platforms"]
+        telegram = next(platform for platform in platforms if platform["id"] == "telegram")
+        assert telegram["name"] == "Telegram"
+        assert telegram["enabled"] is False
+        assert any(field["key"] == "TELEGRAM_BOT_TOKEN" and field["required"] for field in telegram["env_vars"])
+
+    def test_messaging_catalog_covers_gateway_platforms(self):
+        """Catalog is derived from the Platform enum, so every built-in shows up."""
+        from gateway.config import Platform
+
+        resp = self.client.get("/api/messaging/platforms")
+        platforms = {entry["id"] for entry in resp.json()["platforms"]}
+
+        for member in Platform.__members__.values():
+            if member.value == "local":
+                continue
+            assert member.value in platforms, f"Missing gateway platform {member.value} from /api/messaging/platforms"
+
+    def test_messaging_catalog_includes_plugin_platforms(self, monkeypatch):
+        """Plugin-registered adapters appear in the catalog without per-platform code."""
+        from gateway.platform_registry import PlatformEntry, platform_registry
+
+        entry = PlatformEntry(
+            name="ircfake",
+            label="IRC (test)",
+            adapter_factory=lambda cfg: None,
+            check_fn=lambda: True,
+            required_env=["IRC_SERVER"],
+            install_hint="Connect to IRC.",
+            source="plugin",
+        )
+        platform_registry.register(entry)
+        try:
+            resp = self.client.get("/api/messaging/platforms")
+            ids = {row["id"]: row for row in resp.json()["platforms"]}
+            assert "ircfake" in ids
+            assert ids["ircfake"]["name"] == "IRC (test)"
+            assert any(field["key"] == "IRC_SERVER" and field["required"] for field in ids["ircfake"]["env_vars"])
+        finally:
+            platform_registry.unregister("ircfake")
+
+    def test_update_messaging_platform_saves_env_and_enablement(self):
+        from hermes_cli.config import load_config, load_env
+
+        resp = self.client.put(
+            "/api/messaging/platforms/telegram",
+            json={
+                "enabled": False,
+                "env": {"TELEGRAM_BOT_TOKEN": "1234567890abcdef"},
+            },
+        )
+
+        assert resp.status_code == 200
+        assert load_env()["TELEGRAM_BOT_TOKEN"] == "1234567890abcdef"
+        assert load_config()["platforms"]["telegram"]["enabled"] is False
+
+        status = self.client.get("/api/messaging/platforms").json()["platforms"]
+        telegram = next(platform for platform in status if platform["id"] == "telegram")
+        assert telegram["enabled"] is False
+
+    def test_messaging_platform_test_reports_missing_required_setup(self):
+        resp = self.client.put("/api/messaging/platforms/discord", json={"enabled": True})
+        assert resp.status_code == 200
+
+        resp = self.client.post("/api/messaging/platforms/discord/test")
+
+        assert resp.status_code == 200
+        data = resp.json()
+        assert data["ok"] is False
+        assert data["state"] == "not_configured"
+        assert "DISCORD_BOT_TOKEN" in data["message"]
+
     def test_session_token_endpoint_removed(self):
         """GET /api/auth/session-token should no longer exist (token injected via HTML)."""
         resp = self.client.get("/api/auth/session-token")