refactor(projman): normalize RFC to sub-command pattern, absorb clear-cache

- Created unified /rfc command with create|list|review|approve|reject sub-commands
- Deleted 5 individual rfc-*.md command files
- Moved /clear-cache into /setup --clear-cache
- Updated all cross-references in skills, docs, and integration files
- Command count: 17 -> 12 (net -5)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

plugins/projman/skills/rfc-templates.md

@@ -11,7 +11,7 @@ Provides templates for RFC wiki pages and defines the required/optional sections
 
 ## When to Use
 
-- **Commands**: `/rfc-create` when generating new RFC pages
+- **Commands**: `/rfc create` when generating new RFC pages
 - **Integration**: Referenced by `rfc-workflow.md` for page structure
 
 ---