feat: add project export and import functionality

- Implemented `pcli project export` command to export project hierarchy as JSON.
- Added `pcli project import` command to import project data from JSON.
- Created user client to fetch user details for comment attribution.
- Introduced new data structures for export and import processes.
- Ensured name-based references in exports and handled conflicts during imports.
- Added versioning and progress reporting for import operations.
- Updated documentation and specifications for new features.

.windsurf/skills/openspec-archive-change/SKILL.md

@@ -6,7 +6,7 @@ compatibility: Requires openspec CLI.
 metadata:
   author: openspec
   version: "1.0"
-  generatedBy: "1.1.1"
+  generatedBy: "1.2.0"
 ---
 
 Archive a completed change in the experimental workflow.
@@ -63,7 +63,7 @@ Archive a completed change in the experimental workflow.
    - If changes needed: "Sync now (recommended)", "Archive without syncing"
    - If already synced: "Archive now", "Sync anyway", "Cancel"
 
-   If user chooses sync, execute /opsx:sync logic (use the openspec-sync-specs skill). Proceed to archive regardless of choice.
+   If user chooses sync, use Task tool (subagent_type: "general-purpose", prompt: "Use Skill tool to invoke openspec-sync-specs for change '<name>'. Delta spec analysis: <include the analyzed delta spec summary>"). Proceed to archive regardless of choice.
 
 5. **Perform the archive**