[feat](trx-client): persist 24h decode history across restarts

Add pickledb-backed persistent history store for all decoder types
(AIS, VDES, APRS, CW, FT8, WSPR). History is loaded from
~/.local/cache/trx-rs/history.db at startup and flushed to disk
every 60 seconds. On load, entry timestamps are reconstructed from
stored Unix ms values so 24h pruning continues to work correctly.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Signed-off-by: Stan Grams <sjg@haxx.space>

Cargo.lock

@@ -2461,6 +2461,7 @@ dependencies = [
  "cpal",
  "dirs",
  "opus",
+ "pickledb",
  "serde",
  "serde_json",
  "tokio",