Extends GET /api/analytics/wardriving with a payload-anomaly detector:
every "MM:<base64>" message is checked against the standard 7-byte
anonymous session token (confirmed empirically against live traffic).
Non-standard lengths or undecodable payloads are grouped per sender
as a candidate signal that MeshMapper's optional "Broadcast My
Coordinates" mode is active — surfaced as a raw hex dump, never
interpreted as lat/lon, since that mode's byte format is undocumented.
Messages without the "MM:" prefix (plain channel chat) are ignored
entirely rather than polluting either bucket.
Frontend adds a Payload Anomalies table plus a stat card, completing
all 6 originally-proposed wardriving analytics ideas.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
