testing.html: Reset Zoom and ⏸ Pause buttons don't work

[jonathaneoliver]

Summary

On content/dashboard/testing.html, the Reset Zoom and ⏸ Pause / Live buttons in the bitrate chart toolbar do nothing when clicked.

Repro

1. Open http://localhost:30000/dashboard/testing.html (or test-dev :21000).
2. Pick a session with an active bitrate chart.
3. Click Reset Zoom — nothing happens.
4. Click ⏸ Pause — nothing happens (label never flips to Live, no PAUSED overlay appears).

Likely cause

Both buttons are rendered by content/dashboard/testing-session-ui.js:

• testing-session-ui.js:1090 — <button data-action="reset-bitrate-zoom">Reset Zoom</button>
• testing-session-ui.js:1091 — <button data-action="pause-bitrate-chart">⏸ Pause</button>

testing-session.html wires them up in its click delegate:

• testing-session.html:3951 — handles reset-bitrate-zoom
• testing-session.html:3964 — handles pause-bitrate-chart

But testing.html's click delegate at testing.html:5183 has cases for apply-pattern, edit-pattern, add-shaping-step, clear-shaping-pattern, save-session, delete-session, etc. — and no cases for reset-bitrate-zoom or pause-bitrate-chart. The pause-state helpers (toggleChartPause, updatePauseButtonAndOverlays, installLiveWheelAnchor) exist in testing.html (lines ~2347–2407) and are wired to a chart-canvas click handler, but the toolbar buttons themselves are never bound.

Proposed fix

Add handlers in testing.html's click delegate that mirror testing-session.html:3951–3978:

• reset-bitrate-zoom → look up the chart and call chart.resetZoom('none').
• pause-bitrate-chart → call the existing toggleChartPause(sessionId).

Per the project convention (Cross-compare testing pages), keep behavior in sync with testing-session.html.

[jonathaneoliver]

Points: 2 (Fibonacci)
Effort: ~30–45 min (code) + ~15 min deploy/verify = ~1 hr total
Priority: P2 — next sprint; buttons are broken but the underlying data and overlays still render, so no session is blind
Value: medium — affects every testing.html user who tries to zoom or pause a bitrate chart, but the workaround is to open testing-session.html directly

Rationale: The fix is two switch cases, each one-liner, mirroring already-tested code in testing-session.html. Surface area is minimal. P2/medium because this is a testing-tool convenience regression, not a core streaming or playback defect.