Initial MCM project: FastAPI + Textual TUI unified messenger

MultiCustomerMessenger supporting Telegram (python-telegram-bot),
WhatsApp (Green API) and SMS (python-gsmmodem-new). REST API with
Bearer-token auth, SQLAlchemy models for MariaDB, APScheduler for
background polling, and Textual TUI running in same asyncio event-loop.

tui/screens/compose_screen.py

@@ -0,0 +1,50 @@
+from __future__ import annotations
+
+from textual.app import ComposeResult
+from textual.containers import Horizontal, Vertical
+from textual.screen import ModalScreen
+from textual.widgets import Button, Input, Label, Select, TextArea
+
+
+CHANNEL_OPTIONS = [
+    ("Telegram", "telegram"),
+    ("WhatsApp", "whatsapp"),
+    ("SMS", "sms"),
+]
+
+
+class ComposeScreen(ModalScreen[dict | None]):
+    """Modal-Dialog für neue ausgehende Nachricht."""
+
+    DEFAULT_CSS = ""
+
+    def compose(self) -> ComposeResult:
+        with Vertical(id="compose-dialog"):
+            yield Label("Neue Nachricht", id="compose-title")
+            yield Label("Kanal:")
+            yield Select(
+                [(label, value) for label, value in CHANNEL_OPTIONS],
+                id="channel-select",
+                value="telegram",
+            )
+            yield Label("Empfänger (Telefon / Telegram-ID):")
+            yield Input(placeholder="+49… oder Telegram-Chat-ID", id="recipient-input")
+            yield Label("Nachricht:")
+            yield TextArea(id="msg-textarea")
+            with Horizontal(id="compose-buttons"):
+                yield Button("Abbrechen", variant="default", id="btn-cancel")
+                yield Button("Senden", variant="primary", id="btn-send")
+
+    def on_button_pressed(self, event: Button.Pressed) -> None:
+        if event.button.id == "btn-cancel":
+            self.dismiss(None)
+            return
+
+        channel = self.query_one("#channel-select", Select).value
+        recipient = self.query_one("#recipient-input", Input).value.strip()
+        text = self.query_one("#msg-textarea", TextArea).text.strip()
+
+        if not recipient or not text:
+            return
+
+        self.dismiss({"channel": channel, "recipient": recipient, "text": text})