[codex] Add keybinding conflict warnings

[bendsp]

Summary

• detect duplicate normalized keybindings across configured actions
• show conflict warnings directly in the keybinding settings rows
• add unit coverage for conflict detection and unique binding behavior

Validation

• pnpm lint
• pnpm typecheck
• pnpm test:unit

[Copilot]

Pull request overview

Adds duplicate-keybinding detection to the renderer so users can see conflicts directly in the Settings modal, with accompanying unit tests to prevent regressions.

Changes:

• Added findKeyBindingConflicts() to detect duplicate normalized bindings across actions.
• Updated keybinding settings rows to display a per-action “Conflicts with …” warning.
• Added unit tests for conflict detection and wired them into the unit test entrypoint.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
tests/keybindings.test.ts	Adds unit coverage for conflict detection and the no-conflicts case.
tests/index.ts	Registers the new keybindings unit test file in the test runner.
src/renderer/keybindings.ts	Adds findKeyBindingConflicts() and hardens platform detection for non-browser runtimes.
src/renderer/components/SettingsModal.tsx	Computes conflicts from current settings and renders conflict warnings in keybinding rows.

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