[Agent] Merge LiveView and WebRTCView into one Live component

Problem and evidence

The Live page has two near-duplicate components that have to be kept in sync by hand:

web/js/components/preact/LiveView.jsx (~1,110 lines) and web/js/components/preact/WebRTCView.jsx (~1,131 lines). Their operator surface, building plan, detection overlay, slideshow, grid and auto-grid code is nearly identical.
web/js/pages/index-page.jsx:~85-105 picks one at runtime: WebRTCView unless WebRTC is disabled.
Bugs have had to be fixed twice (for example the placeholder shown until auto-grid resolves, LiveView.jsx:~185 and WebRTCView.jsx:~187), and features land in one view and get missed in the other.

Merge the two into one LiveView component that renders the right cell type for the active transport (WebRTC, HLS, MSE or Auto). The cell components (WebRTCVideoCell, HLSVideoCell, MSEVideoCell) stay as they are.
Before changing anything, diff the two files and list every real behavioral difference in the PR description (transport tab handling, auto-fallback, audio, etc.). Each one must be kept, behind the transport switch.
index-page.jsx renders the single component. Delete WebRTCView.jsx.
Update tests and imports that refer to WebRTCView.

With every combination of webrtcDisabled, hlsDisabled, mseDisabled and autoDisabled from /api/client-config, the visible tabs and the default transport match current behavior.
Slideshow, building plan, operator surface, detection overlays, PTZ, fullscreen, PiP and the grid picker work on every transport.
The net line count drops substantially (expect −900 or more).
No new i18n keys are needed. Reuse the existing ones.

cd web && npx vite build, npm run lint, npm test, and the npm run test:e2e live-view specs if they apply.
Add a Jest test that renders the merged view under each transport-flag combination and checks the tabs.
Manual smoke test in a browser against a running instance with at least two cameras.