feat(usage): plan usage limits header chip via statusLine telemetry

Surface Claude subscription plan usage limits (5-hour rolling + 7-day
weekly: percent used + reset time) in the header, opt-in via App Settings
→ Display → "Plan Usage Limits" (default OFF, no behavior change when off).

A Codeman-managed Claude statusLine exporter forwards the rate_limits JSON
to a new auth-exempt POST /api/status-telemetry (same loopback + hook-secret
gate as /api/hook-event); parsed telemetry broadcasts over SSE
session:statusTelemetry to a header chip (amber >=80%, red >=95%, reset
times on hover). The exporter prints the same summary back as the
in-terminal footer (print-through).

- src/usage-telemetry.ts: pure parser/formatter (epoch-sec -> ms, clamp,
  change signature) + test/usage-telemetry.test.ts
- hooks-config.ts: generateStatusLineCommand + applyStatusLineConfig
  (add/remove; never clobbers a user's own statusLine)
- session-routes.ts: inject gate (Claude-only, Codeman-managed cases),
  driven by create-payload statusLineTelemetry (session-ui.js)
- schemas.ts: StatusTelemetrySchema + showPlanUsageLimits + payload field
- frontend: header chip, applyHeaderVisibilitySettings toggle,
  renderIndexHtml strip, _onSessionStatusTelemetry handler

Schema empirically confirmed against Claude Code 2.1.177 (Claude Max):
only five_hour/seven_day windows exist (no Opus-weekly field); rate_limits
is absent before the first API response and for non-subscriber auth. Design
+ verification method in docs/usage-limits-display-plan.md.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/web/public/index.html

@@ -115,6 +115,7 @@
         </div>
         <button class="btn-icon-header btn-response-viewer-header btn-response-viewer-header--hidden" onclick="app.toggleResponseViewer()" title="View last response" aria-label="View last response"><svg width="16" height="16" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2"><path d="M1 12s4-8 11-8 11 8 11 8-4 8-11 8-11-8-11-8z"/><circle cx="12" cy="12" r="3"/></svg></button>
         <button class="btn-icon-header btn-multimonitor btn-multimonitor--hidden" onclick="app.launchMultiMonitor()" title="Open Codeman across all displays" aria-label="Open Codeman across all displays"><svg width="16" height="16" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round" aria-hidden="true"><rect x="2" y="4" width="13" height="9" rx="1.5"/><rect x="11" y="9" width="11" height="8" rx="1.5"/></svg></button>
+        <div class="header-plan-usage header-plan-usage--hidden" id="planUsageChip" title="Claude plan usage limits">—</div>
         <button class="btn-icon-header btn-notifications" onclick="app.toggleNotifications()" title="Notifications" aria-label="Toggle notifications" style="display:none;">
           <svg width="16" height="16" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round" aria-hidden="true"><path d="M18 8A6 6 0 0 0 6 8c0 7-3 9-3 9h18s-3-2-3-9"/><path d="M13.73 21a2 2 0 0 1-3.46 0"/></svg>
           <span class="notification-badge" id="notifBadge" style="display:none;">0</span>
@@ -1025,6 +1026,13 @@
                   <span class="slider"></span>
                 </label>
               </div>
+              <div class="settings-item" title="Show Claude plan usage limits (5-hour & weekly) in the header. Applies to newly created sessions.">
+                <span class="settings-item-label">Plan Usage Limits</span>
+                <label class="switch switch-sm">
+                  <input type="checkbox" id="appSettingsShowPlanUsageLimits">
+                  <span class="slider"></span>
+                </label>
+              </div>
 
               <!-- Tab Bar Section -->
               <div class="settings-section-header">Tab Bar</div>