feat(shared): implement shared data architecture (v3.1.0)

Phase 1: Multi-profile shared data via symlinks

Added:

- SharedManager class for symlink orchestration (bin/shared-manager.js)

- Auto-migration from ~/.claude/ to ~/.ccs/shared/ on first run

- Shared directories: commands/, skills/, agents/

- Windows fallback: copies dirs if symlinks fail

Fixed:

- Migration logic now detects empty directories

- Previously skipped migration when postinstall created empty dirs

- Now properly copies from ~/.claude/ when shared dirs are empty

Changed:

- Instance initialization symlinks to shared dirs instead of copying

- Postinstall creates ~/.ccs/shared/ structure automatically

- All implementations (Node.js, bash, PowerShell) updated for consistency

- Help text includes agents/ in shared data section

Technical:

- Profile-specific data remains isolated (settings, sessions, todolists, logs)

- Migration is idempotent: safe to run multiple times

- Cross-platform symlink support with graceful fallback

Closes #4

package.json

@@ -1,6 +1,6 @@
 {
   "name": "@kaitranntt/ccs",
-  "version": "3.0.2",
+  "version": "3.1.0",
   "description": "Claude Code Switch - Instant profile switching between Claude Sonnet 4.5 and GLM 4.6",
   "keywords": [
     "cli",