ADV_TYPE_ROOM=3 (0b0011) was misread as chat+repeater because decoder
treated lower nibble as individual bits. Now correctly: type & 0x0F as
enum (0=none, 1=chat, 2=repeater, 3=room, 4=sensor).
Includes startup backfill: scans all adverts and fixes any node roles
in the DB that were incorrectly set to 'repeater' when they should be
'room'. Logs count of fixed nodes on startup.
Timestamp is decoded from the ADVERT but never persisted to the nodes
table. The validation was rejecting valid nodes with slightly-off clocks
(28h future) and nodes broadcasting timestamp=4. No reason to gate on it.
