feat(config): make assistants configuration project-scoped

[8nevil8]

Summary

Implements EPMCDME-10896. Allows users to save assistant registrations at the project level (.codemie/codemie-cli.config.json) instead of only globally (~/.codemie/codemie-cli.config.json). A new scope selection screen appears in the codemie setup assistants flow after configuring registration modes. Project-scoped config overrides global; global remains the fallback for projects without local config.

Changes

• src/utils/config.ts — New ConfigLoader.saveAssistantsToProjectConfig() method: updates only the codemieAssistants field in the local config file (creates file if absent), preserving all other local profile fields.
• src/cli/commands/assistants/setup/index.ts — Scope selection screen (raw-mode TUI, same pattern as promptModeSelection) inserted before applyChanges. Guards against showing the prompt when no changes are detected. Uses the class-level LOCAL_CONFIG constant for the save path.
• src/cli/commands/assistants/constants.ts — New message constants for the scope prompt UI and summary output.
• src/cli/commands/assistants/setup/summary/index.ts — displaySummary now accepts and displays configLocation (global or local path).

Impact

Before: codemie setup assistants always saved to ~/.codemie/codemie-cli.config.json regardless of context.

After: Users are prompted with a full-screen TUI selection:

  Where would you like to save assistant configuration?

  ● Global (~/.codemie/) - Available across all projects
  ○ Local  (.codemie/) - Only for this project

  ↑↓ Navigate   Enter Confirm

Selecting Local writes only the codemieAssistants field to .codemie/codemie-cli.config.json in the current repository. Existing global-only users pressing Enter (default = Global) are unaffected.

Checklist

• Self-reviewed
• Manual testing performed
• Documentation updated (if needed)
• No breaking changes (or clearly documented)