feat: add plugin support to shared directories (v4.3.6) (#15)

* feat(shared): add plugin support to shared directories

Add Claude Code plugins to the .ccs/shared/ symlink architecture,
enabling plugin sharing across all CCS profiles (GLM, GLMT, Kimi, etc).

Changes:
- SharedManager: Add 'plugins' to sharedDirs array
- Help text: Update all three implementations (Node.js, bash, PowerShell)
- Postinstall: Create ~/.ccs/shared/plugins/ directory on install

Architecture:
~/.claude/plugins/ <- ~/.ccs/shared/plugins/ <- instance/plugins/

This follows the existing pattern for commands/skills/agents and
maintains cross-platform compatibility with Windows fallback support.

* chore: bump version to 4.3.6

* docs: update CHANGELOG for v4.3.6

scripts/postinstall.js

@@ -81,7 +81,7 @@ function createConfigFiles() {
     }
 
     // Create shared subdirectories
-    const sharedSubdirs = ['commands', 'skills', 'agents'];
+    const sharedSubdirs = ['commands', 'skills', 'agents', 'plugins'];
     for (const subdir of sharedSubdirs) {
       const subdirPath = path.join(sharedDir, subdir);
       if (!fs.existsSync(subdirPath)) {