Add recorder: raw CAN and GNSS sessions with failsafes and a storage bound

Reads SocketCAN and gpsd directly. Sessions start on the first frame or on
'ctl start', end after 15 s of bus idle or on 'ctl stop'; blips under 3 s are
discarded. candump -L chunks fdatasync'd every second and zstd'd once closed;
oldest sessions deleted to stay under 50 GB / above 20 GB free. Kernel and
queue drops, link changes and clock steps are recorded as events.

Bench-tested on vcan with the first car capture (byte-identical) and installed
on the car Orin as yukart-recorder.service.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01DDwfd6Ki8UfG4hK6W5YpJz

Cargo.toml

@@ -0,0 +1,19 @@
+[package]
+name = "svc-core"
+version = "0.1.0"
+edition = "2021"
+description = "Acquisition and processing cluster: recorder now; can-bridge, obd-poller, gnss, decoder later"
+publish = false
+
+[[bin]]
+name = "recorder"
+path = "src/recorder/main.rs"
+
+[dependencies]
+libc = "0.2"
+serde_json = "1"
+signal-hook = "0.3"
+zstd = "0.13"
+
+[profile.release]
+strip = true