fix(settings): improve keybind binding UX (OPEN-54)

[zortos293]

Summary

Addresses OPEN-54 by making shortcut configuration in Settings and the stream sidebar easier and safer.

Changes

• Press-to-bind: Shortcut fields are read-only; focus the field and press the desired key combination to bind (Escape blurs without saving invalid state from partial typing).
• Paste: Clipboard paste still works via explicit onPaste handlers (needed because read-only inputs often block default paste).
• Duplicate detection: Saving or capturing a shortcut now rejects conflicts with any other editable binding and with the fixed stream sidebar toggle (Meta+G on macOS, Ctrl+Shift+G elsewhere), matching the actual handler in StreamView.
• Recording shortcut in Settings: shortcutToggleRecording was already persisted but had no Settings UI; it is now editable alongside the others and included in reset-to-defaults.
• Stream sidebar shortcuts tab: Screenshot/recording fields use the same capture flow; conflict checks now include Anti-AFK; sidebar toggle display uses formatShortcutForDisplay with canonical Meta+G on Mac.
• UX: Replaced <label> wrappers around inputs with separate labels so clicking the label text no longer steals focus from the adjacent field. Read-only bind fields use a pointer cursor in CSS.

Testing

• npm install and npx tsc --noEmit for both tsconfig.node.json and tsconfig.json (pass).

Linear Issue: OPEN-54