fix(migration): run migration during install, not on first execution (v3.1.1)

Fixed:

- Migration now runs during installation across all methods (npm, bash, PowerShell)

- Guarantees ~/.ccs/shared/ populated immediately with ~/.claude/ content

- Users no longer need to run ccs command to trigger migration

Changed:

- Refactored SharedManager with _needsMigration() and _performMigration() methods

- _copyDirectory() returns {copied, skipped} stats and preserves existing files

- Shows detailed migration output: '[OK] Migrated 5 commands, 19 skills'

- Removed lazy migration from bin/ccs.js, lib/ccs, lib/ccs.ps1

Implementation:

- npm: Migration in scripts/postinstall.js

- bash: Migration in installers/install.sh (migrate_shared_data function)

- PowerShell: Migration in installers/install.ps1 (Invoke-SharedDataMigration)

- Fixed arithmetic expansion with set -e (changed ((var++)) to var=$((var + 1)))

Cross-platform parity maintained across all installation methods.

scripts/postinstall.js

@@ -89,6 +89,18 @@ function createConfigFiles() {
       }
     }
 
+    // Migrate from ~/.claude/ to ~/.ccs/shared/ (v3.1.1)
+    console.log('');
+    try {
+      const SharedManager = require('../bin/shared-manager');
+      const sharedManager = new SharedManager();
+      sharedManager.migrateToSharedStructure();
+    } catch (err) {
+      console.warn('[!] Migration warning:', err.message);
+      console.warn('    You can manually copy files from ~/.claude/ to ~/.ccs/shared/');
+    }
+    console.log('');
+
     // Create config.json if missing
     const configPath = path.join(ccsDir, 'config.json');
     if (!fs.existsSync(configPath)) {