Verify autotune knobs against hardware before sweeping

Sweeping a knob the driver ignores measures nothing but benchmark noise, and the
tuner would then confidently report 'best = the highest value tried'. On this box
(driver 595.84) nvidia-settings accepts GPUGraphicsClockOffset/GPUMemoryTransferRate
Offset and silently discards them: assigning 0 reports success and reads back 250.
The ollama profile's core_offset_mhz=35 and mem_offset_mhz=200 have therefore been
doing nothing.

- _knob_effective() applies a probe value and confirms the hardware actually moved
  before any sweep starts, choosing the candidate furthest from the current reading
  (probing with the maximum fails when the card already sits at its top clock).
- Adds discrete clock-lock knobs (lock_mem_mhz, lock_core_max) driven by the card's
  own supported-clock list, since -lmc/-lgc do work where offsets do not.
- Reasoning models return their output in 'thinking' with an empty 'response', which
  the degeneracy check was flagging as corruption. Token count is now the primary
  signal.
- Separates gain-vs-current-setting from gain-vs-slowest-value-tried. Reporting the
  latter as 'gain vs baseline' implied a +102% speedup that nobody would observe.

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

static/app.js

@@ -855,7 +855,11 @@ function renderSweep(d) {
   const best = d.best
     ? `<div class="text-emerald-400 mb-2">★ Best stable: <span class="font-mono">${d.knob}=${d.best.value}</span>
        → ${d.best.tokens_per_sec} tok/s at ${d.best.temp_c}°C
-       ${d.gain_pct != null ? `<span class="text-slate-400">(${d.gain_pct > 0 ? '+' : ''}${d.gain_pct}% vs baseline)</span>` : ''}
+       ${d.gain_vs_current_pct != null
+           ? `<span class="text-slate-400">(${d.gain_vs_current_pct > 0 ? '+' : ''}${d.gain_vs_current_pct}% vs your current setting)</span>`
+           : d.gain_vs_first_step_pct != null
+             ? `<span class="text-slate-500">(spread across tried values: ${d.gain_vs_first_step_pct > 0 ? '+' : ''}${d.gain_vs_first_step_pct}% vs slowest)</span>`
+             : ''}
        ${d.applied_to_profile ? '<span class="text-fuchsia-400">· saved to profile</span>' : ''}</div>`
     : '<div class="text-amber-400 mb-2">No stable step produced throughput.</div>';
   const unstable = d.first_unstable