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/styles.tcss

@@ -0,0 +1,128 @@
+/* MCM TUI Stylesheet */
+
+Screen {
+    background: $surface;
+}
+
+/* ── Haupt-Layout ─────────────────────────────────────────────────────── */
+
+#main-container {
+    layout: horizontal;
+    height: 1fr;
+}
+
+/* ── Seitenleiste (Konversationsliste) ────────────────────────────────── */
+
+#sidebar {
+    width: 28;
+    min-width: 22;
+    max-width: 40;
+    border-right: solid $primary-darken-1;
+}
+
+#sidebar-title {
+    background: $primary;
+    color: $text;
+    text-style: bold;
+    padding: 0 1;
+    height: 1;
+}
+
+#conv-list {
+    height: 1fr;
+}
+
+#conv-list > DataTable {
+    height: 1fr;
+    scrollbar-gutter: stable;
+}
+
+/* ── Chat-Bereich ─────────────────────────────────────────────────────── */
+
+#chat-area {
+    width: 1fr;
+    layout: vertical;
+}
+
+#chat-header {
+    height: 1;
+    background: $primary-darken-1;
+    color: $text;
+    padding: 0 1;
+    text-style: bold;
+}
+
+#message-log {
+    height: 1fr;
+    border: none;
+    padding: 0 1;
+    scrollbar-gutter: stable;
+}
+
+#input-bar {
+    height: auto;
+    min-height: 3;
+    border-top: solid $primary-darken-1;
+    padding: 0 1;
+    layout: horizontal;
+}
+
+#msg-input {
+    width: 1fr;
+    border: none;
+}
+
+#send-btn {
+    width: 10;
+    min-width: 8;
+    margin-left: 1;
+}
+
+/* ── Kanal-Badges ─────────────────────────────────────────────────────── */
+
+.badge-telegram  { color: $accent; }
+.badge-whatsapp  { color: $success; }
+.badge-sms       { color: $warning; }
+
+/* ── Nachrichten ──────────────────────────────────────────────────────── */
+
+.msg-inbound  { color: $text; }
+.msg-outbound { color: $text-muted; }
+.msg-failed   { color: $error; }
+
+/* ── Compose Modal ────────────────────────────────────────────────────── */
+
+#compose-dialog {
+    width: 70;
+    height: auto;
+    border: thick $primary;
+    background: $surface;
+    padding: 1 2;
+}
+
+#compose-dialog Label {
+    margin-top: 1;
+}
+
+#compose-dialog Select {
+    width: 100%;
+}
+
+#compose-dialog Input {
+    width: 100%;
+}
+
+#compose-dialog TextArea {
+    width: 100%;
+    height: 6;
+}
+
+#compose-buttons {
+    layout: horizontal;
+    margin-top: 1;
+    align: right middle;
+}
+
+#compose-buttons Button {
+    margin-left: 1;
+}