DSMR hardening: restart-free config + decouple from telegram id

Config hot-reload (no restart):
- MqttManager.unsubscribe(); apply_dsmr_subscription(settings) re-applies the
  DSMR subscription (subscribe/unsubscribe/topic-change, fresh snapshot so the
  sample interval also takes effect).
- Called from lifespan AND PUT /api/config, so toggling DSMR ingest in the UI
  takes effect immediately without restarting the app.

Decouple ingest from the DSMR telegram id (overflows / resets to zero):
- Migration 20260624_12: drop UNIQUE(source_id), make recorded_at UNIQUE.
- Idempotency now keys on recorded_at (telegram timestamp); the table's own
  autoincrement PK is the stable identity. source_id kept only as a reference.
- Regression test: colliding telegram ids no longer drop new data.

tests/test_dsmr_ingest.py

@@ -214,12 +214,12 @@ def test_off_interval_not_multiple_of_10(dsmr_db):
 
 
 # ---------------------------------------------------------------------------
-# 3. Idempotency — same source_id not re-inserted
+# 3. Idempotency — keyed on recorded_at (telegram timestamp), NOT the telegram id
 # ---------------------------------------------------------------------------
 
 
-def test_same_source_id_not_reinserted(dsmr_db):
-    """Feeding the same telegram twice (same id) must result in exactly one row."""
+def test_same_timestamp_not_reinserted(dsmr_db):
+    """Feeding the same telegram twice (same timestamp) must result in one row."""
     _, SessionLocal = dsmr_db
     settings = _make_settings(dsmr_sample_interval_s=10)
 
@@ -229,8 +229,8 @@ def test_same_source_id_not_reinserted(dsmr_db):
     assert _count_readings(SessionLocal) == 1
 
 
-def test_different_source_ids_are_independent(dsmr_db):
-    """Different id values from different telegrams produce separate rows."""
+def test_different_timestamps_are_independent(dsmr_db):
+    """Telegrams with different timestamps produce separate rows."""
     _, SessionLocal = dsmr_db
     settings = _make_settings(dsmr_sample_interval_s=10)
 
@@ -240,6 +240,24 @@ def test_different_source_ids_are_independent(dsmr_db):
     assert _count_readings(SessionLocal) == 2
 
 
+def test_telegram_id_collision_does_not_drop_new_data(dsmr_db):
+    """Regression: the telegram id overflows / gets reset to zero in DSMR firmware.
+    Two DISTINCT telegrams (different timestamps) that happen to share the SAME
+    telegram id must BOTH be stored — dedup must not depend on the telegram id."""
+    _, SessionLocal = dsmr_db
+    settings = _make_settings(dsmr_sample_interval_s=10)
+
+    first = {**_SAMPLE_TELEGRAM, "id": 0, "timestamp": "2026-06-23T12:16:00Z"}
+    # Later telegram, id reset back to the same value after an overflow.
+    second = {**_SAMPLE_TELEGRAM, "id": 0, "timestamp": "2026-06-23T12:16:10Z"}
+
+    _call_handle_message(first, settings, SessionLocal)
+    _call_handle_message(second, settings, SessionLocal)
+
+    # Both must persist — the colliding telegram id must not cause a drop.
+    assert _count_readings(SessionLocal) == 2
+
+
 # ---------------------------------------------------------------------------
 # 4. Missing source_id — still persisted with source_id=None
 # ---------------------------------------------------------------------------