feat(gateway): add Telegram adapter and formatting

surfsense_backend/tests/unit/gateway/test_formatting.py

@@ -0,0 +1,18 @@
+from app.gateway.telegram.formatting import chunk_message, escape_markdown_v2
+
+
+def test_escape_markdown_v2_reserved_chars():
+    text = r"_*[]()~`>#+-=|{}.!"
+
+    assert escape_markdown_v2(text) == r"\_\*\[\]\(\)\~\`\>\#\+\-\=\|\{\}\.\!"
+
+
+def test_chunk_message_preserves_content_and_limits_size():
+    text = "First paragraph.\n\n" + ("x" * 5000)
+
+    chunks = chunk_message(text, max_units=4096)
+
+    assert "".join(chunks) == text
+    assert len(chunks) > 1
+    assert all(len(chunk.encode("utf-16-le")) // 2 <= 4096 for chunk in chunks)
+