feat(cliproxy): extend composite schema with fallback and thinking fields

- Add fallback? (provider+model) to CompositeTierConfig for per-tier retry
- Add thinking? string to CompositeTierConfig for per-tier thinking budget
- Add hasFallback flag to VariantConfig for runtime detection
- Propagate new fields in listVariantsFromConfig()

Refs #506

src/cliproxy/services/variant-config-adapter.ts

@@ -41,6 +41,8 @@ export interface VariantConfig {
     sonnet: CompositeTierConfig;
     haiku: CompositeTierConfig;
   };
+  /** Whether any tier has fallback configured */
+  hasFallback?: boolean;
 }
 
 /**
@@ -100,13 +102,20 @@ export function listVariantsFromConfig(): Record<string, VariantConfig> {
         const v = variants[name];
         if ('type' in v && v.type === 'composite') {
           const composite = v as CompositeVariantConfig;
+          const tiers = composite.tiers;
+          const hasFallback = !!(
+            tiers.opus.fallback ||
+            tiers.sonnet.fallback ||
+            tiers.haiku.fallback
+          );
           result[name] = {
-            provider: composite.tiers[composite.default_tier].provider,
+            provider: tiers[composite.default_tier].provider,
             settings: composite.settings,
             port: composite.port,
             type: 'composite',
             default_tier: composite.default_tier,
-            tiers: composite.tiers,
+            tiers,
+            hasFallback,
           };
         } else {
           const single = v as CLIProxyVariantConfig;

src/config/unified-config-types.ts

@@ -97,6 +97,14 @@ export interface CompositeTierConfig {
   model: string;
   /** Account nickname (optional, references oauth_accounts) */
   account?: string;
+  /** Fallback provider+model if primary fails */
+  fallback?: {
+    provider: 'gemini' | 'codex' | 'agy' | 'qwen' | 'iflow' | 'kiro' | 'ghcp' | 'claude';
+    model: string;
+    account?: string;
+  };
+  /** Per-tier thinking budget override (e.g. 'xhigh', 'medium', 'off') */
+  thinking?: string;
 }
 
 /**