Add lap timer UI controls page

[bracyw]

Changes

Adds a Lap Timer page to the Angular client — a stopwatch-style interface for managing laps during field deployments. The page has start/pause/stop/lap/reset controls, live telemetry gauges (speed, battery SOC, motor temp), and a scrollable lap list with per-lap stats and delta-from-best highlighting. A root-provided service manages timer state using requestAnimationFrame for smooth sub-second updates, records telemetry snapshots per lap (avg speed, energy used, max motor temp), and persists across navigation. API calls are stubbed and fire-and-forget since the backend endpoints don't exist yet.

New files include the page component (lap-timer-page), a lap timer service, a lap timer API stub, and URL constants. Modified app-routing and the nav bar to register the route and add a nav entry.

Notes

• Best/worst lap highlighting uses left-border color (green/red) following motorsport UI conventions
• Grid layout uses mat-grid-list consistent with other pages
• Telemetry subscriptions stay active during pause to avoid subscribe/unsubscribe churn
• Component uses OnPush with signals for efficient change detection

Test Cases

• Start timer, verify total and lap counters increment in real time
• Pause timer, verify counters freeze; resume, verify they continue
• Record multiple laps, verify lap list populates in reverse-chronological order
• Stop timer, verify final partial lap is recorded and state returns to idle
• Reset after stop, verify all laps and counters are cleared
• Best lap gets green highlight, worst gets red; deltas show +/- from best
• Session stats panel shows correct lap count, best time, average, and energy used
• Edge case: hitting Lap immediately after Start (zero-duration lap) is ignored
• Edge case: stopping with no laps recorded still works cleanly
• Edge case: navigating away and back — timer keeps running (root service persists)

To Do

• Backend endpoints for lap timer persistence (Lap Timer UI Controls #547 follow-up)
• Unit tests for LapTimerService

Checklist

• All commits are tagged with the ticket number
• No linting errors / newline at end of file warnings
• All code follows repository-configured prettier formatting
• No merge conflicts
• All checks passing
• Screenshots of UI changes
• No package-lock.json changes (unless dependencies have changed)
• Request reviewers & ping on Slack
• PR is linked to the ticket

Closes #547