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

package.json

@@ -1,6 +1,6 @@
 {
   "name": "@kaitranntt/ccs",
-  "version": "4.3.5",
+  "version": "4.3.6",
   "description": "Claude Code Switch - Instant profile switching between Claude Sonnet 4.5 and GLM 4.6",
   "keywords": [
     "cli",