feat: TUI als Browser-App via textual serve

TUI von direkten Service-Importen auf httpx API-Calls umgestellt.
Neue tui/api_client.py als schlanker async HTTP-Client. Background-
Worker pollt API alle 5s für Echtzeit-Updates. Neuer tui_standalone.py
Entry-Point für 'textual serve --port 8001 tui_standalone.py'.

tui/api_client.py

@@ -0,0 +1,94 @@
+"""Async HTTP-Client für die MCM REST-API.
+
+Die TUI kommuniziert ausschließlich über diesen Client mit dem Backend.
+Dadurch läuft die TUI sowohl im Terminal (python main.py) als auch im
+Browser (textual serve tui_standalone.py) ohne Änderung.
+"""
+
+from __future__ import annotations
+
+import logging
+from typing import Any
+
+import httpx
+
+from config import settings
+
+logger = logging.getLogger(__name__)
+
+
+class MCMApiClient:
+    """Thin async wrapper um die MCM REST-API."""
+
+    def __init__(self) -> None:
+        self._base = f"http://127.0.0.1:{settings.port}/api/v1"
+        self._headers = {"Authorization": f"Bearer {settings.api_key}"}
+
+    # ── Konversationen ─────────────────────────────────────────────────────────
+
+    async def get_conversations(self, channel: str | None = None) -> list[dict[str, Any]]:
+        params: dict[str, Any] = {}
+        if channel:
+            params["channel"] = channel
+        return await self._get("/conversations", params=params)
+
+    async def get_conversation(self, conv_id: str) -> dict[str, Any] | None:
+        try:
+            return await self._get(f"/conversations/{conv_id}")
+        except httpx.HTTPStatusError:
+            return None
+
+    async def get_messages(
+        self, conv_id: str, limit: int = 100, offset: int = 0
+    ) -> list[dict[str, Any]]:
+        return await self._get(
+            f"/conversations/{conv_id}/messages",
+            params={"limit": limit, "offset": offset},
+        )
+
+    # ── Nachrichten senden ─────────────────────────────────────────────────────
+
+    async def send_message(
+        self,
+        channel: str,
+        text: str,
+        recipient_phone: str | None = None,
+        recipient_telegram_id: str | None = None,
+        reply_to_id: str | None = None,
+    ) -> dict[str, Any]:
+        body: dict[str, Any] = {"channel": channel, "text": text}
+        if recipient_phone:
+            body["recipient_phone"] = recipient_phone
+        if recipient_telegram_id:
+            body["recipient_telegram_id"] = recipient_telegram_id
+        if reply_to_id:
+            body["reply_to_id"] = reply_to_id
+        return await self._post("/messages", body)
+
+    # ── Kontakte ───────────────────────────────────────────────────────────────
+
+    async def get_contacts(self) -> list[dict[str, Any]]:
+        return await self._get("/contacts")
+
+    # ── Status ─────────────────────────────────────────────────────────────────
+
+    async def get_channel_status(self) -> dict[str, Any]:
+        return await self._get("/channels/status")
+
+    # ── Interne Hilfsmethoden ──────────────────────────────────────────────────
+
+    async def _get(self, path: str, params: dict | None = None) -> Any:
+        async with httpx.AsyncClient(timeout=5.0, follow_redirects=True) as client:
+            resp = await client.get(
+                self._base + path, headers=self._headers, params=params
+            )
+            resp.raise_for_status()
+            return resp.json()
+
+    async def _post(self, path: str, body: dict) -> Any:
+        async with httpx.AsyncClient(timeout=10.0, follow_redirects=True) as client:
+            resp = await client.post(
+                self._base + path, headers=self._headers, json=body
+            )
+            resp.raise_for_status()
+            return resp.json()