feat: persistent sessions, remove track_map use case, car characteristics DB

- Remove obsolete TrackMap use case variant (superseded by TrackMapping)
- Add session/run/analysis persistence: metadata to data/sessions/<id>.json,
  frames to <id>.frames.json (split for lazy loading)
- Atomic writes (temp + rename), compact JSON, off-thread frame serialization
- load_all loads metadata only at startup; ensure_frames_loaded lazy-loads
  frames before analysis
- Normalize Recording runs to Stopped on reload (stale ring-buffer markers)
- Cache car_name on UseCaseSession during run finalization
- Add characteristics.rs: aggregate shift-point data per car across sessions
- New API: GET /api/characteristics/cars, GET /api/characteristics/cars/{car}
- Add Deserialize to TelemetryFrame and FeedSource for session round-trip

src/telemetry_frame.rs

@@ -3,10 +3,10 @@
 //! Both the KSUDP (port 9996) and Telemetry Tool (port 10101) parsers produce
 //! `TelemetryFrame` instances from their raw binary data.
 
-use serde::Serialize;
+use serde::{Deserialize, Serialize};
 
 /// Identifies which feed source produced this frame.
-#[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize)]
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize, Deserialize)]
 pub enum FeedSource {
     Ksudp,
     TelemetryTool,
@@ -20,7 +20,7 @@ pub const NUM_WHEELS: usize = 4;
 ///
 /// Fields present in both feeds are stored directly; fields unique to one feed
 /// are wrapped in `Option`.
-#[derive(Debug, Clone, Serialize)]
+#[derive(Debug, Clone, Serialize, Deserialize)]
 pub struct TelemetryFrame {
     // ── Speed ──────────────────────────────────────────────────────
     pub speed_kmh: f32,