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

Move persistent history from trx-client to trx-server where decode
events originate. History for AIS, VDES, APRS, CW, FT8, and WSPR is
loaded from ~/.local/cache/trx-rs/history.db at startup and flushed
to disk every 60 seconds. CW events are now also stored in
DecoderHistories and replayed to connecting clients, consistent with
all other decoder types.

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

src/trx-server/Cargo.toml

@@ -21,6 +21,7 @@ toml = { workspace = true }
 tracing = { workspace = true }
 clap = { workspace = true, features = ["derive"] }
 dirs = "6"
+pickledb = "0.5"
 chrono = { version = "0.4", default-features = false, features = ["clock"] }
 bytes = "1"
 cpal = "0.15"