feat(dashboard): shared range bar, sensitivity control, drill breadcrumb (PR-B)

[surpradhan]

What does this PR do?

Builds on PR-A (#151) with analytics UX improvements and session drill-through. Stacked on feat/dashboard-nav-polish — will rebase to main once #151 merges.

Changes

Shared range bar — replaces three duplicate per-view toolbars (Policy Analytics, Performance, Anomalies) with a single range bar shown above the Analyze sub-nav. All three views read from shared-since/shared-until. Range persists as you switch sub-tabs within Analyze.

change-trigger — when both Since and Until inputs are set, the active view auto-loads. No more mandatory Apply click for range changes. Explicit Apply and quick-range buttons still work.

Sensitivity control — the z-score threshold (ad-threshold) was previously buried inline with the Anomalies range toolbar. It's now a dedicated "Sensitivity (z-score)" section that appears only on the Anomalies sub-tab — semantically separate from the time range.

Custom Analytics untouched — Custom keeps its own cq-since/cq-until controls and explicit "Run query" button. The shared range bar is hidden on the Custom sub-tab.

Drill breadcrumb — drillSession() now captures the source view, encodes it as #sessions?from=analytics in the URL (survives back-navigation), and shows a "← Back to Policy Analytics" breadcrumb inside the Sessions panel. applyInitialHash() restores the breadcrumb on reload.

Why?

Three identical toolbars forced the user to reconfigure the range every time they switched sub-tabs. Hiding the threshold inside the range bar implied it was a time value. No breadcrumb left users stranded after drilling into a session from Performance or Anomalies.

How to test?

ADMIN_TOKEN=dev-admin npm run ingest
open http://localhost:8787/dashboard

1. Navigate to Analyze → Policy Analytics — shared range bar appears
2. Set a 1h range, click Apply — loads filtered data
3. Switch to Performance sub-tab — same range still set, auto-loads
4. Navigate to Analyze → Anomalies — Sensitivity control appears below the range bar
5. Navigate to Analyze → Custom Analytics — shared range bar disappears, Custom's own controls visible
6. In Performance: click "Go to session" on any result — Sessions panel shows "← Back to Performance" breadcrumb
7. Click the breadcrumb — returns to Performance view
8. Navigate to #sessions?from=analytics directly — breadcrumb appears without drilling

Checklist

• Tests pass (239/239)
• Single file changed (src/public/dashboard.html)
• No new CI job
• No dangling an-since/pf-since/ad-since references
• Stacked on feat/dashboard-nav-polish (feat(dashboard): two-level nav, live ticker, and polish (PR-A) #151)

[surpradhan]

Round 1 findings (all addressed in ceec8a0): (1) drillOrigin set after switchMain in both drillSession and applyInitialHash — fixed by moving the assignment before the call; (2) no guard for mainView === 'sessions' drill — fixed; (3) indentation nit on inner .layout div — fixed. Round 2: all three fixes are correct, no new issues, tests 239/0. Approve.

[surpradhan]

Round 1 findings (all addressed in ceec8a0): (1) drillOrigin set after switchMain in both drillSession and applyInitialHash — fixed by moving the assignment before the call; (2) no guard for mainView === 'sessions' drill — fixed; (3) indentation nit on inner .layout div — fixed. Round 2: all three fixes are correct, no new issues, tests 239/0. Approve.