Convert the packets table to a time-partitioned table with daily
partitions (PARTITION BY RANGE on received_at). This replaces the
expensive CTE-based batch DELETE cleanup with instant DROP TABLE
partition drops — no dead tuples, no WAL pressure, no VACUUM needed.
- Add PartitionManager GenServer to create/drop daily partitions
- Simplify PacketCleanupWorker to delegate to PartitionManager
- Replace gridsquare/geocalc deps with local Maidenhead module
- Remove gettext_pseudolocalize dependency
- Fix Decimal comparison in packet consumer test
