Resource self-protection + back-pressure (eviction budget, load-shedding, GUI watchdog)

[rolker]

Part of #154.

Summary

The "teeth" — consume the ResourceMonitor snapshot (child 1) and keep camp from
crashing under resource pressure, instead of relying on the OS OOM/VRAM-alloc
failure (which killed camp on salmon, #153).

Scope

• Eviction budget feed — expose the monitor's self-accounted GPU/RAM totals as
  the budget the live-cache eviction (Live tile cache is unbounded -> memory/VRAM exhaustion (crashed camp on salmon after enabling live data) #153) consumes (evict until under budget,
  persist-then-drop). This is the concrete first consumer.
• Load-shedding / back-pressure — as a configurable soft limit is approached,
  force-evict and/or stop accepting new live tiles (drop with a logged WARN) rather
  than allocating into a crash. A hard limit triggers aggressive shed + ERROR.
• GUI responsiveness watchdog — a timer that should tick every N s on the GUI
  thread; if it's late by a threshold, flag camp as hung/stalled (event loop
  blocked) even though the process hasn't crashed. Surfaced via diagnostics (child
  3) and the status dot (child 4).

Health levels (OK / WARN / ERROR) derived here from the snapshot + thresholds, fed
to children 3 and 4.

Depends on

Child 1 (the snapshot). Drives #153 (eviction).

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