Smart Context file nav actions

Part of the Smart Context Clipboard feature.
What this surface is for
File navigator actions optimize speed when scope is chosen from folders/files first.
Core actions
- Right-click folder -> Copy folder contents to clipboard.
- Multi-select files -> Copy selected notes as context.
- Multi-select folders/files -> Open selection in Context Builder.
How to choose
- Need fastest export now -> use direct copy actions.
- Need to prune/reorder scope first -> open Context Builder.
- Need tree-only export -> use link-tree copy action where available.
Workflow examples
- Sprint handoff: select spec + task notes -> copy selected notes -> paste into chat.
- Folder kickoff: right-click project folder -> copy folder contents -> run planning prompt.
- Curated delegation: open selection in builder -> trim noise -> copy final bundle.