feat(ui): unify picker Tab/Enter/Shift+Enter and allow directory attachments

[codenomadbot]

Implements the updated keyboard-driven picker behaviors for directory mentions/navigation.

Behavior changes

• Tab / Enter / Shift+Enter are now distinct actions while the Unified Picker is open (packages/ui/src/components/unified-picker.tsx).
• Directories (packages/ui/src/components/prompt-input/usePromptPicker.ts):
  • Tab: autocomplete directory name and keep navigating (shows directory contents via picker query update).
  • Enter: attach the directory as a file attachment with mime: inode/directory (sent as a FilePart pointing at a file://... directory URL).
  • Shift+Enter: attach the directory path as text only (no contents).
• Files:
  • Tab: autocomplete file path only (no attachment).
  • Enter: attach file (existing behavior).
  • Shift+Enter: attach file path as text only (no contents).

Notes

• This does not yet include recursive directory filename listing in the outgoing context; that likely requires backend support (server-side expansion of a directory FilePart, or a dedicated recursive listing endpoint).

Changeset

• packages/ui/src/components/unified-picker.tsx
• packages/ui/src/components/prompt-input/usePromptPicker.ts

Test status

• Unable to run npm run typecheck here because dependencies are not installed in this bot workspace (tsc fails resolving packages like solid-js, zod, etc.).

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Yours, CodeNomadBot