feat(telemetry): report process CPU and FDs plus host memory and load

docs/roadmap.md

@@ -56,8 +56,10 @@ or current fleet size. Metric labels should remain bounded; no per-device labels
 ## Process And Host Visibility
 
 - [x] Add Linux process age/RSS and host uptime gauges for agent and CC through opt-in OTLP, using the existing collection interval. Core owns OS-independent instruments; wakey-linux supplies the optional procfs reader. Missing data omits observations; no added labels, config fields, health routes or polling tasks. Collector coverage verifies units and values; router/live dashboard validation pending.
-- [ ] Extend process measurements with CPU time and open file descriptors where supported, plus start-time/version metadata if needed. Keep version as resource metadata rather than repeating it on every sample.
-- [ ] Add a small host summary: hostname, OS/kernel, CPU count, host uptime, load, and available/total memory. Distinguish host uptime from process uptime so router reboots and agent restarts are visible separately. Sources must tolerate missing Linux files; not every agent host is a router.
+- [x] Add cumulative process CPU time (counter) and current open-FD count (gauge) through the same Linux reader and OS-independent instruments. Exclude child processes, omit failed samples, and document one-core CPU-rate interpretation and sampling FD overhead. Extend collector/reader coverage rather than adding timing-based tests; live validation pending.
+- [ ] Add start-time/version metadata if needed. Keep version as resource metadata rather than repeating it on every sample.
+- [x] Add total/available host memory and 1/5/15-minute load gauges through the optional Linux reader, with byte conversion owned by procfs and fixed load-period labels. Omit unavailable MemAvailable instead of substituting free memory; document kernel views versus container limits. Collector/reader coverage included; live validation pending.
+- [ ] Complete a small host summary with hostname, OS/kernel and CPU count, plus protected UI presentation of collected measurements. Sources must tolerate missing Linux files; not every agent host is a router.
 - [ ] Expose changing measurements through OTLP on a modest sampling interval; show selected process/host details on Fleet Health and agent details. Keep host information behind the protected operator interface, not public health endpoints. Avoid expensive reads on every request and unbounded labels.
 - [ ] Keep `/healthz` as cheap liveness; consider a separate bounded `/readyz` database-access check for CC. Collector outages and disconnected fleet agents must not make a functioning CC unready.
 - [ ] Add application resource gauges where useful: DB pool usage, connected agents, pending commands, and active terminal sessions. Check existing instruments first to avoid duplicates; distinguish pool pressure from host/process pressure.