feat(indicator): add option to always display the indicator near the mouse cursor

[gum798]

Purpose

Add an opt-in way to keep the input source indicator always visible and glued to the mouse pointer, the way Windows' IME badge follows the cursor. Today the indicator either pops up briefly on app / input-source changes, or (with Enhanced Mode) stays near the text caret. Users who want to glance at the current input source at any time, without Accessibility permission, had no option.

Loosely related to #61, which asks about positioning the always-on dot, though that one is about the text caret.

What changes

• New setting "Always Display Indicator Near the Mouse Cursor" under Position, shown only while Follow Mouse is selected (it is a sub-option of that mode). Default off.
• While on:
  • the indicator stays visible and tracks the pointer in real time (global + local NSEvent mouse monitors, throttled to ~60 Hz); it appears immediately when the toggle is switched on and disappears immediately when switched off;
  • it needs no Accessibility / Enhanced Mode;
  • it shows the current input source, and the function-key badge for one second after a toggle, like the transient indicator does;
  • it re-renders when indicator style, size or per-keyboard colours change in Settings;
  • it hides for apps / sites with a "Hide Indicator" rule;
  • it is re-ordered front on Space changes so it follows across Spaces;
  • the text-caret options under Advanced are greyed out since they do not apply.
• The activate-event pipeline stays idle while the mode is on, so nothing else moves or hides the indicator.
• IndicatorPosition.pointNearMouse extracts the near-mouse geometry (offset + screen clamping) that the existing one-shot Follow Mouse placement used, so both paths share it. Covered by new unit tests.
• NSEvent.watch no longer force-unwraps the monitor on teardown.
• Preference is wired through settings backup / restore; strings added for en, ja, ko, zh-Hans, zh-Hant.

Testing

• xcodebuild -scheme "Input Source Pro" -configuration Debug test: 55 tests pass (4 new in IndicatorNearMousePointTests).
• Manually on macOS 26.5 (Xcode 26.6), with an ad-hoc signed build that has no Accessibility permission:
  • indicator tracks the pointer at the 12 pt offset on every move; clamps at screen edges and on a secondary display;
  • toggle on shows it immediately, toggle off hides it immediately;
  • switching ABC ↔ 2-Set Korean updates the content in place (verified with screenshots after each switch);
  • with the option off, the transient indicator behaves exactly as before (appears on switch, gone after ~1 s);
  • CPU stays under ~8 % while sweeping the pointer at 100 Hz, 0 % when idle.

Notes for review

• Turning the option off re-subscribes the shared activate-event stream, which replays the current app once, so the normal indicator shows for one second, the same thing that happens at launch and after unlock. Left as is; suppressing it would change that existing behaviour or leave in-flight timers fighting the pinned indicator.
• The two Advanced toggles keep their stored values; they are only disabled while this mode is effective.

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https://claude.ai/code/session_01PYfrZ8oYRfkLjVXUBF5BHA