Add database-level payload dedupe

app/database.py

@@ -50,12 +50,14 @@ CREATE TABLE IF NOT EXISTS raw_packets (
     timestamp INTEGER NOT NULL,
     data BLOB NOT NULL,
     message_id INTEGER,
+    payload_hash TEXT,
     FOREIGN KEY (message_id) REFERENCES messages(id)
 );
 
 CREATE INDEX IF NOT EXISTS idx_messages_conversation ON messages(type, conversation_key);
 CREATE INDEX IF NOT EXISTS idx_messages_received ON messages(received_at);
 CREATE INDEX IF NOT EXISTS idx_raw_packets_message_id ON raw_packets(message_id);
+CREATE UNIQUE INDEX IF NOT EXISTS idx_raw_packets_payload_hash ON raw_packets(payload_hash);
 CREATE INDEX IF NOT EXISTS idx_contacts_on_radio ON contacts(on_radio);
 """