fix: make the event monitor self-healing and surface Secure Input

[lukas-runge]

Hi @gentlespoon,

after reproducing this a bunch of times I let @claude finally have a look at it. Currently testing it, but seems to work fine. Feel free to also have a look and refine if you have any other ideas on why the frequent event monitor restarts have been necessary since my last PR.

Best regards,
@lukas-runge

Problem

The event monitor regularly died and needed a manual restart via the menu. Separately, sometimes right-click activation kept working while the activation key (Space) appeared dead.

Root causes

1. Tap disabled by macOS, never re-enabled. The tap is an active filter, so every matched event waits on our callback. The callback did synchronous AX IPC on every click system-wide and on every leftMouseDragged event (hundreds/sec), with the default AX messaging timeout of ~6 s per call to a busy app. Once a callback exceeded the tap's time budget, macOS sent tapDisabledByTimeout — which fell into the default: switch case, so the tap stayed dead until a manual restart.

2. Secure Event Input. While any app holds Secure Input (browser password fields, Terminal's Secure Keyboard Entry, password managers), the WindowServer withholds keyboard events from event taps while mouse events keep flowing — exactly the "right-click works, Space doesn't" asymmetry. Not a code bug, but the app gave no indication of it.

Changes (one commit each, in order)

1. Re-enable the tap when tapDisabledByTimeout / tapDisabledByUserInput arrives in the callback.
2. Watchdog (5 s): re-enables a disabled tap, tears down an invalidated mach port, and starts the monitor once accessibility trust exists (covers login autostart before permission is granted, silent tapCreate failure, trust loss after re-signing). isMonitoring now reports the real tap state; trust-loss restart no longer runs inside the tap callback.
3. Cap AX messaging timeout at 250 ms so a single beachballing app can no longer stall the callback past the tap's time budget.
4. Cut callback load: drop unhandled mouseMoved/keyUp from the event mask; stop polling the AX window position on every drag event (the drag state is recomputed on demand in startSnapping(), so behavior is unchanged).
5. Remove force unwraps from the snapping flow — frontMostWindow can legitimately be nil and crashed the app before.
6. Detect Secure Input in the watchdog, log which app holds it, and switch the status bar icon with an explanatory tooltip while it is active.
7. Remove dead code (unused polling, isSpacePressed, unused private CGS API declarations).

Testing

Manually tested on macOS 15: snapping via Space and right-click (with and without moveOnActivate), Escape cancel, multi-monitor drags, and the Secure Input flow (Terminal → Secure Keyboard Entry → status bar indicator appears within ~5 s, Space blocked while right-click keeps working, everything reverts on release).

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