feat: add use-case session management, analysis algorithms, and REST API (v0.5.0)

- Add session layer with UseCaseSession, SessionRun, SessionManager
  for use-case driven telemetry analysis (shift points, track mapping)
- Add analysis module with shift point detection (gear RPM ranges,
  upshift events, recommended shift RPM) and track map reconstruction
  (spline-aligned interpolation for center line from boundary runs)
- Add 9 REST API endpoints for session CRUD, run management, and
  analysis triggers under /api/sessions/*
- Add RecordingManager with always-on ring buffers (5 min, 18k frames)
  replacing raw binary file dumps
- Wire SessionManager in main.rs with Arc<Mutex> shared state
- Add TelemetryFrame Serialize derives for JSON API output
- Fix stop_recording race: hold active lock across flush I/O
- Fix flush: separate ring buffer lock from JSON serialization
- Fix flush failure propagation: errors prevent Stopped status
- Add data_truncated flag on SessionRun for ring buffer wrap detection
- Deduplicate gear_display into shared free function
- Deduplicate session_display into closure
- Mutex poisoning recovery on all session API handlers

src/telemetry_frame.rs

@@ -3,8 +3,10 @@
 //! Both the KSUDP (port 9996) and Telemetry Tool (port 10101) parsers produce
 //! `TelemetryFrame` instances from their raw binary data.
 
+use serde::Serialize;
+
 /// Identifies which feed source produced this frame.
-#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize)]
 pub enum FeedSource {
     Ksudp,
     TelemetryTool,
@@ -18,7 +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)]
+#[derive(Debug, Clone, Serialize)]
 pub struct TelemetryFrame {
     // ── Speed ──────────────────────────────────────────────────────
     pub speed_kmh: f32,
@@ -233,10 +235,15 @@ impl TelemetryFrame {
 
     /// Gear display: 0=Reverse, 1=Neutral, 2+=Gear N-1
     pub fn gear_display(&self) -> String {
-        match self.gear {
-            0 => "R".to_string(),
-            1 => "N".to_string(),
-            n => format!("{}", n - 1),
-        }
+        gear_display(self.gear)
+    }
+}
+
+/// AC gear encoding: 0=Reverse, 1=Neutral, 2+=Gear N-1.
+pub fn gear_display(gear: i32) -> String {
+    match gear {
+        0 => "R".to_string(),
+        1 => "N".to_string(),
+        n => format!("{}", n - 1),
     }
 }