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/workflows/opsx-ff.md

@@ -84,7 +84,10 @@ After completing all artifacts, summarize:
 - Follow the `instruction` field from `openspec instructions` for each artifact type
 - The schema defines what each artifact should contain - follow it
 - Read dependency artifacts for context before creating new ones
-- Use the `template` as a starting point, filling in based on context
+- Use `template` as the structure for your output file - fill in its sections
+- **IMPORTANT**: `context` and `rules` are constraints for YOU, not content for the file
+  - Do NOT copy `<context>`, `<rules>`, `<project_context>` blocks into the artifact
+  - These guide what you write, but should never appear in the output
 
 **Guardrails**
 - Create ALL artifacts needed for implementation (as defined by schema's `apply.requires`)