Hotkey capture field silently freezes when Accessibility permission is missing

**Describe the bug**
When Hex doesn't have Accessibility permission, the hotkey setting field enters
the "Enter a key combination" state but never captures any input — it just freezes
there. There's no indication that a missing permission is the cause, so it reads
as a hung/broken UI rather than a permissions problem. Granting Accessibility
manually and restarting Hex fixes it completely.

**To Reproduce**
Steps to reproduce the behavior:
1. Launch Hex without granting (or after revoking) Accessibility permission. In my
case Hex didn't appear in System Settings → Privacy & Security → Accessibility
at all, and I had to add it manually with the "+" button.
2. Open Settings and click the hotkey field to set a combination.
3. The field switches to "Enter a key combination".
4. Press any key/combo (e.g. Option, or Command+Option) — nothing is captured.

**Expected behavior**
Either the pressed combination is captured, or the field shows a message
explaining that Accessibility permission is required — ideally with a button to
open the relevant System Settings pane — instead of silently freezing.

**Screenshots**
[Optional — a shot of the frozen "Enter a key combination" field would help, if easy]

**Desktop (please complete the following information):**
- macOS: [e.g. Sequoia 15.x]
- Hex version: [e.g. 0.2.11 — menu bar → About]
- Apple Silicon

**Additional context**
Not sure whether the first-launch permission prompt appeared and I dismissed it,
or whether it never fired — so this report focuses on the silent-freeze behavior,
which is reproducible regardless of how the permission ends up missing. Suggested
fix: detect missing Accessibility permission in the hotkey-capture UI and surface
it inline rather than leaving the field frozen.

No files or tests are named. Start in the Settings hotkey-capture UI and reproduce the capture flow with Accessibility permission missing, then trace how permission state is handled. Done means the field no longer silently freezes: it either captures input when permitted or explains the missing permission and offers a way to open the relevant System Settings pane.

Written by the indexing model from the issue text.