ResourceMonitor core — self-sampled footprint + GPU-byte accounting

[rolker]

Part of #154.

Summary

The measurement substrate + single source of truth for camp's own resource
footprint. Pure measurement, no policy — self-protection (#154 child 2), ROS
diagnostics (child 3), and the status-bar gauge (child 4) all consume its snapshot.

Scope

A ResourceMonitor (likely in camp_map core, Qt-only, no ROS) that samples on a
QTimer (configurable interval, e.g. 1 s):

• RSS — /proc/self/status VmRSS (portable, cheap).
• CPU% — /proc/self/stat utime+stime deltas over the sample window.
• threads — /proc/self/task count; open FDs — /proc/self/fd count.
• GPU bytes (self-accounted) — a running counter every texture alloc/free
  updates (R32F × dims × count, LUTs, RGBA8 chart textures). This is the
  load-bearing VRAM number — portable (works on salmon's GPU and llvmpipe) and is
  exactly what bounds the live cache.
• (optional) driver VRAM total/available where the extension exists
  (GL_NVX_gpu_memory_info / GL_ATI_meminfo) as a sanity cross-check only —
  non-portable, not load-bearing.

Exposes:

• a ResourceSnapshot struct (the values above + a timestamp),
• a snapshotUpdated(ResourceSnapshot) signal,
• a registration seam so texture-owning code (raster renderer, live cache) reports
  alloc/free deltas into the GPU counter from one place.

Out of scope (later children)

No thresholds, eviction, load-shedding, diagnostics, or UI here — just truth.

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Authored-By: Claude Code Agent
Model: Claude Opus 4.8