Context menu shortcuts and sort dialog

[bgareth]

The PR addresses a number of weaknesses:

• A11y / keyboard shortcuts for context menu
• Sort dialog visual and a11y issues

Related issue: #758

Changes include:

Keyboard shortcuts for context menus (selection-aware + explicit row/column)**

• Added:
  • Cmd/Ctrl + Shift + M -> open context menu for current selection type
  • Cmd/Ctrl + Shift + R -> open row header context menu
  • Cmd/Ctrl + Shift + L -> open column header context menu
• Reused existing context-menu open logic (handleContextMenu) and selection state
• Updated SR shortcut list and locale strings

Key files:

[packages/react/src/components/Workbook/index.tsx](https://file+.vscode-resource.vscode-cdn.net/Users/garethbeukes/.vscode/extensions/openai.chatgpt-0.4.76-darwin-arm64/webview/#)
[packages/core/src/locale/en.ts](https://file+.vscode-resource.vscode-cdn.net/Users/garethbeukes/.vscode/extensions/openai.chatgpt-0.4.76-darwin-arm64/webview/#)
[packages/core/src/locale/es.ts](https://file+.vscode-resource.vscode-cdn.net/Users/garethbeukes/.vscode/extensions/openai.chatgpt-0.4.76-darwin-arm64/webview/#)
[packages/core/src/locale/zh.ts](https://file+.vscode-resource.vscode-cdn.net/Users/garethbeukes/.vscode/extensions/openai.chatgpt-0.4.76-darwin-arm64/webview/#)
[packages/core/src/locale/zh_tw.ts](https://file+.vscode-resource.vscode-cdn.net/Users/garethbeukes/.vscode/extensions/openai.chatgpt-0.4.76-darwin-arm64/webview/#)
[packages/core/src/locale/hi.ts](https://file+.vscode-resource.vscode-cdn.net/Users/garethbeukes/.vscode/extensions/openai.chatgpt-0.4.76-darwin-arm64/webview/#)
[packages/core/src/locale/ru.ts](https://file+.vscode-resource.vscode-cdn.net/Users/garethbeukes/.vscode/extensions/openai.chatgpt-0.4.76-darwin-arm64/webview/#)

Context menu keyboard activation fix

• Fixed keyboard activation so Enter on focused context menu item triggers the same path as mouse click

Key file:

[packages/react/src/components/ContextMenu/Menu.tsx](https://file+.vscode-resource.vscode-cdn.net/Users/garethbeukes/.vscode/extensions/openai.chatgpt-0.4.76-darwin-arm64/webview/#)

Sort modal styling + accessibility fixes

• Fixed text concatenation, eg: Sort range from G3 to G3 now renders with proper spacing.
• Added spacing between Sort by and dropdown.
• Capitalised sort confirm labels where needed (en, es).
• Added Enter handling for sort confirm and dialog close.
• Added dialog accessibility improvements:
  • role="dialog", aria-modal
  • label wiring to sort title
  • Focus trap
  • Escape to close

Key files:

[packages/react/src/components/CustomSort/index.tsx](https://file+.vscode-resource.vscode-cdn.net/Users/garethbeukes/.vscode/extensions/openai.chatgpt-0.4.76-darwin-arm64/webview/#)
[packages/react/src/components/CustomSort/index.css](https://file+.vscode-resource.vscode-cdn.net/Users/garethbeukes/.vscode/extensions/openai.chatgpt-0.4.76-darwin-arm64/webview/#)
[packages/react/src/components/Dialog/index.tsx](https://file+.vscode-resource.vscode-cdn.net/Users/garethbeukes/.vscode/extensions/openai.chatgpt-0.4.76-darwin-arm64/webview/#)
[packages/core/src/locale/en.ts](https://file+.vscode-resource.vscode-cdn.net/Users/garethbeukes/.vscode/extensions/openai.chatgpt-0.4.76-darwin-arm64/webview/#)
[packages/core/src/locale/es.ts](https://file+.vscode-resource.vscode-cdn.net/Users/garethbeukes/.vscode/extensions/openai.chatgpt-0.4.76-darwin-arm64/webview/#)

Manual Test Checklist

• Cell menu shortcut:
  • Select a cell/range, press Cmd+Shift+M, verify cell context menu opens
• Row menu shortcut:
  • Select any cell in target row, press Cmd+Shift+R, verify row header menu opens
• Column menu shortcut:
  • Select any cell in target column, press Cmd+Shift+L, verify column header menu opens
• Context menu keyboard action:
  • Open context menu, tab to Insert 1 column right, press Enter, verify action runs and no runtime error
• Sort modal spacing/text:
  • Open custom sort, verify title spacing (Sort range from X to Y) and Sort by spacing before dropdown
  • Sort modal keyboard:
    • Press Enter on Sort button -> apply sort
    • Press Enter on close icon -> close
    • Press Esc -> close
    • Tab/Shift+Tab cycles focus within dialog only

yarn eslint on touched files: pass
yarn tsc: pass