Fix slash command menu selection behavior

[zhengdaqi]

Summary

• Make slash command suggestions insert the command into the composer instead of auto-submitting selected skill commands.
• Build one display-order command list shared by keyboard navigation and rendered menu rows.
• Keep pinned/frequent/builtin/project/user/other grouping while preventing arrow-key highlight jumps.

Verification

• npx eslint src/components/chat/hooks/useSlashCommands.ts src/components/chat/hooks/useChatComposerState.ts src/components/chat/view/subcomponents/CommandMenu.tsx
  • passes with 0 errors; existing warnings remain in useChatComposerState.ts
• npx tsc --noEmit --jsx react-jsx --target ES2020 --lib ES2020,DOM,DOM.Iterable --module ESNext --moduleResolution Bundler --skipLibCheck --strict --allowJs --types vite/client src/types/global.d.ts src/components/chat/hooks/useSlashCommands.ts src/components/chat/hooks/useChatComposerState.ts
• git diff --check