[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>

Cargo.lock

@@ -2461,7 +2461,6 @@ dependencies = [
  "cpal",
  "dirs",
  "opus",
- "pickledb",
  "serde",
  "serde_json",
  "tokio",
@@ -2594,6 +2593,7 @@ dependencies = [
  "dirs",
  "num-complex",
  "opus",
+ "pickledb",
  "serde",
  "serde_json",
  "tokio",