Add custom Vim key mappings

[apples-kksk]

Fixes #464

Summary

• add a persisted general.editorVimKeyMaps preference using the maintainer-suggested { toKeys, keys, context } shape
• add a preferences textarea for JSON Vim mappings, with validation and localized labels
• synchronize saved mappings to CodeMirror Vim via CodeMirror.Vim.map and clear previous mappings with unmap when preferences change

Example value:

[{"toKeys":"jk","keys":"<Esc>","context":"insert"}]

Testing

• npx prettier --check src/cloud/lib/stores/settings/types.ts src/cloud/lib/stores/settings/store.ts src/cloud/lib/editor/CodeMirror.ts src/cloud/lib/editor/components/CodeMirrorEditor.tsx src/cloud/components/settings/UserPreferencesForm.tsx src/cloud/lib/i18n/types.ts src/cloud/lib/i18n/enUS.ts src/cloud/lib/i18n/zhCN.ts src/cloud/lib/i18n/ja.ts src/cloud/lib/i18n/fr.ts
• npx eslint src/cloud/lib/stores/settings/types.ts src/cloud/lib/stores/settings/store.ts src/cloud/lib/editor/CodeMirror.ts src/cloud/lib/editor/components/CodeMirrorEditor.tsx src/cloud/components/settings/UserPreferencesForm.tsx src/cloud/lib/i18n/types.ts src/cloud/lib/i18n/enUS.ts src/cloud/lib/i18n/zhCN.ts src/cloud/lib/i18n/ja.ts src/cloud/lib/i18n/fr.ts --ext .ts,.tsx
• npx tsc --noEmit --pretty false

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IssueHunt Summary

Referenced issues

This pull request has been submitted to:

• #464: Custom vim mappings

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