[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>

src/trx-client/Cargo.toml

@@ -15,6 +15,7 @@ toml = { workspace = true }
 tracing = { workspace = true }
 clap = { workspace = true, features = ["derive"] }
 dirs = "6"
+pickledb = "0.5"
 bytes = "1"
 cpal = "0.15"
 opus = "0.3"