## Summary
Switches channel API endpoints to query SQLite instead of the in-memory
packet store, giving users access to the full message history.
Implements #725 (M1 only — DB-backed channel messages). Does NOT close
#725 — M2-M5 (custom channels, PSK, persistence, retroactive decryption)
remain.
## Problem
Channel endpoints (`/api/channels`, `/api/channels/{hash}/messages`)
preferred the in-memory packet store when available. The store is
bounded by `packetStore.maxMemoryMB` — typically showing only recent
messages. The SQLite database has the complete history (weeks/months of
channel messages) but was only used as a fallback when the store was nil
(never in production).
## Fix
Reversed the preference order: DB first, in-memory store fallback.
Region filtering added to the DB path.
Co-authored-by: you <you@example.com>
