Improve Live Feed navigation responsiveness

[prsmith777]

What changed

• Consolidates Live Feed polling under one controller and makes the Live updates switch authoritative.
• Pauses automatic refresh while the image viewer is open.
• Applies confirm/reopen state locally and defers refresh until the popup closes.
• Handles filtered page-boundary Confirm & Next with one explicit refresh.
• Prefetches adjacent pages and removes the viewer's duplicate image request.
• Adds a bounded browser performance buffer with per-action, page-boundary, camera, read, and image-load timings.
• Updates the help manual, product roadmap, release information, and regression coverage.

Why

Navigation became slow and occasionally timed out after additional cameras were added. The root cause was overlapping refresh work: the wrapper and table each ran independent polling loops, the switch controlled only one local state, review actions raced router refreshes against image navigation, and the viewer loaded the same image twice.

Impact

Next, Previous, and Confirm & Next should respond without waiting on background feed refreshes. The new measurements make same-page, cross-page, and camera-transition latency visible in window.__ALPR_LIVE_FEED_PERFORMANCE__ for staging validation.

No database migration is included.

Validation

• yarn test: 740 tests; 739 passed, 1 skipped, 0 failed
• yarn typecheck: passed
• yarn lint: passed with 6 pre-existing warnings and no errors
• yarn build: passed
• Baseline staging sample before the fix: same-page Next took 297–399 ms across 8 samples; actions overlapping refreshes could exceed the browser's 3-second action timeout.