feat: unify Claude API key and profile system with flexible key sourcing

- Add ApiKeySource type ('inline' | 'env' | 'credentials') to ClaudeApiProfile
- Allow profiles to source API keys from credentials.json or environment variables
- Add provider templates: OpenRouter, MiniMax, MiniMax (China)
- Auto-migrate existing users with Anthropic key to "Direct Anthropic" profile
- Update all API call sites to pass credentials for key resolution
- Add API key source selector to profile creation UI
- Increment settings version to 5 for migration support

This allows users to:
- Share a single API key across multiple profile configurations
- Use environment variables for CI/CD deployments
- Easily switch between providers without re-entering keys

apps/ui/src/components/views/settings-view/api-keys/api-keys-section.tsx

@@ -109,6 +109,15 @@ export function ApiKeysSection() {
         {/* Security Notice */}
         <SecurityNotice />
 
+        {/* Profile Usage Note */}
+        <div className="text-xs text-muted-foreground/80 px-1">
+          <p>
+            API Keys saved here can be used by API Profiles with "credentials" as the API key
+            source. This lets you share a single key across multiple profile configurations without
+            re-entering it.
+          </p>
+        </div>
+
         {/* Action Buttons */}
         <div className="flex flex-wrap items-center gap-3 pt-2">
           <Button