Fix two more stale-cache bugs; account for VRAM this service cannot reclaim

The stale-readback bug fixed in f5917a0 was a class, not an instance. Two more:

- ram_optimizer's residency report cached for 15s and was never invalidated when
  anything warmed a file, so warming a model and then looking at residency showed
  the state from before the warm. warm_file_to_ram now invalidates it.
- _PID_KIND_CACHE was keyed on pid alone and never expired. Linux recycles PIDs, so
  a stale entry could attribute a new process's VRAM to Ollama or ComfyUI -- inside
  the very snapshot the yield barrier trusts to decide whether VRAM was released.
  Now keyed by (pid, process start time) and bounded.

Unmanaged VRAM. Investigating a persistence-mode warning turned up a third GPU
consumer this service does not model: stt_relay.py, holding 842 MB for nearly three
days. It was bucketed as "system" alongside gnome-shell's 3.9 MB. That conflation
matters, because ComfyUI's memory can be reclaimed and a third party's cannot, and
the reclaim path assumed ComfyUI was always to blame for missing headroom.

Processes are now bucketed ollama | comfy | desktop | unmanaged. The breakdown
reports desktop_gb and unmanaged_gb separately and names the unmanaged processes;
when a reclaim-and-retry still fails, the error identifies them rather than
implying ComfyUI was at fault; and the dashboard shows the unreclaimable total, so
headroom the arbitrator can never give back is visible rather than inferred.

Checked and deliberately not changed: persistence mode reads Disabled, but
nvidia-persistenced is active and two clients hold the GPU open continuously, so
the driver never unloads. The nvidia-smi warning is legacy noise here and is not a
source of the profile drift.

Tests: 169 (was 164). The new ones cover the bucketing, and one existing test used
Xorg as its "unknown process" fixture -- correct before a display server had its own
bucket, wrong after.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

static/index.html

@@ -686,6 +686,7 @@
         <div class="mt-4">
           <div id="arb-action" class="text-sm text-slate-200 bg-slate-950/60 border border-slate-800 rounded-lg px-3 py-2 mb-3 font-mono">Idle</div>
           <div id="arb-backoff" class="text-[11px] font-mono text-amber-400 mb-3"></div>
+          <div id="arb-unmanaged" class="text-[11px] font-mono text-slate-400 mb-3"></div>
           <div class="grid grid-cols-3 sm:grid-cols-6 gap-2 text-center">
             <div class="bg-slate-950/60 rounded-lg p-2 border border-slate-800">
               <div id="arb-yields" class="text-lg font-bold text-emerald-400">0</div>