feat: auto-fill OTP verification codes from Android notifications

[aislingheart]

What

Detects one-time verification codes in mirrored Android notifications and copies them to the Mac clipboard for quick pasting (Mac-local only, never synced back to Android).

How

• New OtpCodeExtractor (Core/Util/OTP/): keyword gate (code, otp, verification, 2fa, …) so years/prices/counts never trigger, then matches grouped (123 456, 123-456, 73 91 08) preferred over plain (482910), 4–8 digits, year-like 1900–2099 rejected.
• Hook in AppState.addNotification — the single funnel both WebSocket and BLE already flow through — gated on contentChanged so repeat/ongoing updates don't re-copy.
• New isOtpAutofillEnabled setting (defaults on, persisted), toggle + hint in Sync → Clipboard Sync. Strings in en.json only (Crowdin picks up the rest).

Verification

• AirSync Self Compiled scheme: BUILD SUCCEEDED.
• Extractor behavior harness (compiled + run standalone): 13/13 cases pass (plain/grouped/triple-grouped codes detected; years, prices, non-keyword numbers ignored).
• No protocol changes; no Android changes needed. Overlap checked: no open PR/branch touches this path.