Toggle between modes feature

[davidnkam01]

Hello and thank you for the quality of your work.
Please add a feature that can toggle between modes ( especially direct and mitm script) without need of Start and Stop app.

[therealaleph]

Reviewed via Anthropic Claude.

@davidnkam01 — reasonable feature ask. Currently each mode change requires Stop → edit config → Start. Adding hot-swap: technical sketch:

1. Config already supports all three modes (mode: apps_script | full | google_only | direct) via the same struct.
2. The proxy server (src/proxy_server.rs) currently builds its dispatch table at startup based on the loaded config. Hot-swap requires either:
   • Atomic replace: lock config, drop in-flight connections, build new dispatch, resume — UX equivalent to a fast restart but no port re-bind churn.
   • Per-request mode lookup: each connection reads the current mode from a shared ArcSwap<Config>, so a flip applies to the next connection without dropping anything in flight.

Per-request lookup is the better UX (no traffic interruption). Implementation:

• Wrap Config in arc_swap::ArcSwap<Config> instead of Arc<Config>.
• Each handler reads config.load() at the start of the request.
• UI "Apply" button calls config_holder.store(Arc::new(new_cfg)) — atomic flip.

Real cost: the per-handler load is ~5ns (atomic load), so it's free in practice. The hard part is making sure no handler caches the old config across the await points where the swap can happen (currently most do, since they hold an Arc<Config>).

Queued. Probably lands as a 50-100 line refactor + UI button + an integration test that swaps mode mid-traffic and confirms next request takes the new mode.

Leaving open as the tracking issue.