decoder: broadcast frames to yukart/vehicle/* from contracts' can blocks

Kernel-filtered read-only socket; booleans on change, numbers <= 20/s, every
live value refreshed once a second, stale after 1 s of silence. --replay runs
a candump log through the same path, --list prints the layouts. obd-poller
drops engine_rpm, now a z27ag signal.

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

Cargo.toml

@@ -2,7 +2,7 @@
 name = "svc-core"
 version = "0.1.0"
 edition = "2021"
-description = "Acquisition and processing cluster: recorder, orin-status and obd-poller now; can-bridge, gnss, decoder later"
+description = "Acquisition and processing cluster: recorder, decoder, orin-status and obd-poller now; can-bridge and gnss later"
 publish = false
 
 [[bin]]
@@ -17,6 +17,10 @@ path = "src/orin-status/main.rs"
 name = "obd-poller"
 path = "src/obd-poller/main.rs"
 
+[[bin]]
+name = "decoder"
+path = "src/decoder/main.rs"
+
 [[bin]]
 name = "bus-bench"
 path = "src/bus-bench/main.rs"