Fix OBS icons stuck on error after OBS restart

[f1nalspace]

Problem

When OBS is closed and reopened, the action icons (Record, Stream, etc.)
stay stuck on the error triangle and never recover. The error is shown
correctly while OBS is gone, but the icon does not return to normal once
OBS is reachable again — the page has to be reloaded to recover.

Root cause

Three combined defects (found via logging the connection state across the
frontend and the separate backend process):

1. Tick crash on empty response — when OBS closes, a websocket request
   returns an empty datain, so status.datain["outputActive"] raised
   KeyError, crashing the action tick instead of showing the error cleanly.

2. Unreliable disconnect signal — OBSController.connected stayed True
   because on_disconnect does not reliably fire on a hard OBS shutdown, so
   reconnection was never triggered. The library's own authreconnect also
   competed with the plugin and left the connection in an inconsistent state.

3. Error overlay never cleared — show_error() sets a persistent overlay
   that is only removed by hide_error(). Only ToggleStream called
   hide_error(); every other action left the triangle on top of the normal
   icon even after the connection recovered.

Changes

• backend/backend.py: new build_status_dict() — returns None on a
  missing/empty response and marks the connection as lost (no more KeyError).
• backend/OBSController.py: disable the library auto-reconnect
  (authreconnect=0) and add teardown_existing_connection() for clean
  reconnects.
• OBSActionBase.py: throttled try_reconnect_if_disconnected() driven from
  the tick loop.
• All status actions: call hide_error() in the success path so the error
  overlay clears once OBS is reachable again.

Testing

Verified live: closing OBS shows the error icon; reopening OBS recovers the
correct status icon automatically within a few seconds, no page reload needed.