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

README.md

@@ -0,0 +1,32 @@
+---
+type: reference
+---
+# Core services
+
+Part of **Project Yukart**, making an old 2008 Mitsubishi Z27AG a bit smarter with modern technologies.  
+This file serves as the minimalist portal to other docs
+
+
+## What this repo is about
+
+The acquisition and processing cluster on the Orin, developed and deployed as one
+unit: `recorder` now; `can-bridge`, `obd-poller`, `gnss` and `decoder` as they are
+needed.
+
+| Binary | Installed as | Does |
+|---|---|---|
+| `recorder` | `yukart-recorder.service` | Raw CAN + GNSS to disk, in sessions, under a storage bound |
+
+```bash
+scripts/deploy-recorder.sh                 # build, glibc check, install on the car Orin
+yukart-recorder ctl status                 # on the Orin
+yukart-recorder ctl start "cold start"     # manual session, ends only on stop
+yukart-recorder ctl mark "indicator left on"
+yukart-recorder ctl stop
+```
+
+Recordings live in `/var/lib/yukart/recordings/`, one directory per session —
+layout in [the initial plan](docs/impl/plans/INITIAL.md#session-layout).
+
+- For implementation practice guidelines, refer to the [guidelines](docs/GUIDELINES.md);  
+- For implementation plans and history, refer to [them](docs/impl/);