feat(api): add Anthropic direct API key support

Support native Anthropic API keys (sk-ant-...) via `ccs api create --preset anthropic`.
Profiles use ANTHROPIC_API_KEY env var without BASE_URL, letting Claude CLI
authenticate natively with x-api-key header instead of proxy Bearer token.

- Add anthropic preset to provider catalog
- Branch profile-writer env structure (native vs proxy)
- Add validateAnthropicKey() preflight with x-api-key header
- Auto-detect api.anthropic.com URL in interactive flow
- Fix hasApiKey/isConfigured to recognize ANTHROPIC_API_KEY
- Update delegation-validator for native mode profiles
- Add Droid target API key fallback (ANTHROPIC_API_KEY)

Closes #688

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/api/services/profile-reader.ts

@@ -49,7 +49,7 @@ export function isApiProfileConfigured(apiName: string): boolean {
     if (!fs.existsSync(settingsPath)) return false;
 
     const settings = JSON.parse(fs.readFileSync(settingsPath, 'utf8'));
-    const token = settings?.env?.ANTHROPIC_AUTH_TOKEN || '';
+    const token = settings?.env?.ANTHROPIC_AUTH_TOKEN || settings?.env?.ANTHROPIC_API_KEY || '';
     return token.length > 0 && !token.includes('YOUR_') && !token.includes('your-');
   } catch {
     return false;