fix(projman): remove automatic cache clearing from session start hook

The startup-check.sh hook was clearing ~/.claude/plugins/cache/ at every
session start, which was aggressive and potentially disruptive. Cache
clearing is now a manual operation via the new /clear-cache command.

Changes:
- Remove automatic cache clearing from startup-check.sh
- Add /clear-cache command for manual cache clearing when needed

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

plugins/projman/commands/clear-cache.md

@@ -0,0 +1,24 @@
+# /clear-cache
+
+Clear plugin cache to force fresh configuration reload. Run this after marketplace updates.
+
+## When to Use
+
+- After updating the marketplace (`git pull` or reinstall)
+- When MCP servers show stale configuration
+- When plugin changes don't take effect
+
+## What It Does
+
+1. Clears `~/.claude/plugins/cache/leo-claude-mktplace/`
+2. Forces Claude Code to re-read `.mcp.json` files on next session
+
+## Instructions
+
+Run this command, then **restart your Claude Code session** for changes to take effect.
+
+```bash
+rm -rf ~/.claude/plugins/cache/leo-claude-mktplace/
+```
+
+After clearing, inform the user: "Cache cleared. Restart Claude Code for changes to take effect."