Restructure web UI navigation into 7 numbered workflow stages

Replace the flat menu (Dashboard, Audit, Validate, Burn, Benchmark,
Tasks, Tools) with a numbered progression that guides engineers through
a logical acceptance workflow:

  Dashboard (landing) → 1. Audit → 2. Check → 3. Load → 4. Speed
  → 5. Endurance → 6. Tools → 7. Settings

Key changes:
- layout.go: numbered nav labels, new hrefs, Tasks removed from nav
  and replaced with a persistent sidebar badge (polls /api/tasks every
  5 s, highlights amber when tasks are active)
- server.go: 301 redirects from /validate→/check, /burn→/load,
  /benchmark→/speed for backward compatibility
- pages.go: dispatch cases for all new routes; old routes kept as
  fallbacks
- page_validate.go: add renderCheck() — non-destructive check page
  with validate-mode tests only (no stress toggle, no targeted-stress/
  targeted-power/pulse cards)
- page_burn.go: add renderLoad() wrapper; update scope alert to
  reference /check instead of /validate
- page_benchmark.go: add renderSpeed() (performance focus) and
  renderEndurance() (stability/overnight focus) wrappers
- page_settings.go: new Settings page with blackbox logging toggle,
  NVIDIA driver reset, and build info
- server_test.go: update five tests to use new route names and
  content expectations

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

audit/internal/webui/page_burn.go

@@ -1,8 +1,13 @@
 package webui
 
+// renderLoad renders the Load page (step 3): sustained stress tests.
+// For non-destructive status checks, see Check (step 2).
+// For DCGM targeted diagnostics (targeted_stress, targeted_power, pulse), see Check → Validate mode.
+func renderLoad() string { return renderBurn() }
+
 func renderBurn() string {
 	return `<div class="alert alert-warn" style="margin-bottom:16px"><strong>&#9888; Warning:</strong> Stress tests on this page run hardware at high load. Repeated or prolonged use may reduce hardware lifespan. Use only when necessary.</div>
-<div class="alert alert-info" style="margin-bottom:16px"><strong>Scope:</strong> Burn exposes sustained GPU compute load recipes. DCGM diagnostics (` + "targeted_stress, targeted_power, pulse_test" + `) and LINPACK remain in <a href="/validate">Validate → Stress mode</a>; NCCL and NVBandwidth are available directly from <a href="/validate">Validate</a>.</div>
+<div class="alert alert-info" style="margin-bottom:16px"><strong>Scope:</strong> Load runs sustained GPU compute and CPU/memory stress recipes. DCGM diagnostics (<code>targeted_stress</code>, <code>targeted_power</code>, <code>pulse_test</code>) and NCCL/NVBandwidth are on the <a href="/check">2. Check</a> page. For overnight endurance runs, see <a href="/endurance">5. Endurance</a>.</div>
 <p style="color:var(--muted);font-size:13px;margin-bottom:16px">Tasks continue in the background — view progress in <a href="/tasks">Tasks</a>.</p>
 
 <div class="card" style="margin-bottom:16px">