feat(config): add unified YAML config with migration support

Implements unified config.yaml format consolidating:
- config.json (API profiles)
- profiles.json (account metadata)
- *.settings.json (env vars)

Features:
- Auto-migration from v1 JSON to v2 YAML with backup
- Secrets separation into secrets.yaml (chmod 600)
- Enhanced YAML output with section comments
- CLIProxy OAuth settings migration with env var support
- Feature flag for gradual rollout (CCS_UNIFIED_CONFIG=1)
- Rollback support via ccs migrate --rollback

New commands:
- ccs migrate - Run migration
- ccs migrate --dry-run - Preview changes
- ccs migrate --rollback <path> - Restore from backup
- ccs migrate --list-backups - List available backups

Closes #75

src/ccs.ts

@@ -202,6 +202,10 @@ interface ProfileError extends Error {
 async function main(): Promise<void> {
   const args = process.argv.slice(2);
 
+  // Auto-migrate to unified config format (silent if already migrated)
+  const { autoMigrate } = await import('./config/migration-manager');
+  await autoMigrate();
+
   // Special case: version command (check BEFORE profile detection)
   const firstArg = args[0];
   if (firstArg === 'version' || firstArg === '--version' || firstArg === '-v') {
@@ -245,6 +249,20 @@ async function main(): Promise<void> {
     return;
   }
 
+  // Special case: migrate command
+  if (firstArg === 'migrate' || firstArg === '--migrate') {
+    const { handleMigrateCommand, printMigrateHelp } = await import('./commands/migrate-command');
+    const migrateArgs = args.slice(1);
+
+    if (migrateArgs.includes('--help') || migrateArgs.includes('-h')) {
+      printMigrateHelp();
+      return;
+    }
+
+    await handleMigrateCommand(migrateArgs);
+    return;
+  }
+
   // Special case: update command
   if (firstArg === 'update' || firstArg === '--update') {
     const updateArgs = args.slice(1);