fix(config): migrate all hardcoded paths to getCcsDir() and improve validation

- Replace os.homedir() + '.ccs' with getCcsDir() across 14 instances in 13 files:
  version-command, model-config, openrouter-catalog, config-checks, disk-cache,
  aggregator, auth-middleware, shell-completion, shared-manager, recovery-manager,
  auto-repair, delegation-validator, claude-dir-installer, cliproxy executor
- Add isDirectory() validation for --config-dir argument in ccs.ts
- Make detectCloudSyncPath() case-insensitive for cloud provider matching
- Fix help-command.ts to use dynamic dirDisplay for all path references
- Add 5 new tests: setGlobalConfigDir precedence, relative path resolution,
  reset behavior, getCcsDirSource with --config-dir, case-insensitive detection
- Clean up unused os imports after migration

src/utils/shell-completion.ts

@@ -1,6 +1,7 @@
 import * as fs from 'fs';
 import * as path from 'path';
 import * as os from 'os';
+import { getCcsDir } from './config-manager';
 // import { execSync } from 'child_process'; // Currently unused
 
 type ShellType = 'bash' | 'zsh' | 'fish' | 'powershell' | null;
@@ -24,7 +25,7 @@ export class ShellCompletionInstaller {
 
   constructor() {
     this.homeDir = os.homedir();
-    this.ccsDir = path.join(this.homeDir, '.ccs');
+    this.ccsDir = getCcsDir();
     this.completionDir = path.join(this.ccsDir, 'completions');
     this.scriptsDir = path.join(__dirname, '../../scripts/completion');
   }