feat: add @automaker/model-resolver package

- Extract model string resolution logic
- Map model aliases to full model strings (haiku -> claude-haiku-4-5)
- Handle multiple model sources with priority
- Re-export model constants from @automaker/types

Provides centralized model resolution for Claude models.
Simplifies model handling across server and UI.

Dependencies: @automaker/types

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

libs/model-resolver/src/resolver.ts

@@ -0,0 +1,65 @@
+/**
+ * Model resolution utilities for handling model string mapping
+ *
+ * Provides centralized model resolution logic:
+ * - Maps Claude model aliases to full model strings
+ * - Provides default models per provider
+ * - Handles multiple model sources with priority
+ */
+
+import { CLAUDE_MODEL_MAP, DEFAULT_MODELS } from '@automaker/types';
+
+/**
+ * Resolve a model key/alias to a full model string
+ *
+ * @param modelKey - Model key (e.g., "opus", "gpt-5.2", "claude-sonnet-4-20250514")
+ * @param defaultModel - Fallback model if modelKey is undefined
+ * @returns Full model string
+ */
+export function resolveModelString(
+  modelKey?: string,
+  defaultModel: string = DEFAULT_MODELS.claude
+): string {
+  // No model specified - use default
+  if (!modelKey) {
+    return defaultModel;
+  }
+
+  // Full Claude model string - pass through unchanged
+  if (modelKey.includes("claude-")) {
+    console.log(`[ModelResolver] Using full Claude model string: ${modelKey}`);
+    return modelKey;
+  }
+
+  // Look up Claude model alias
+  const resolved = CLAUDE_MODEL_MAP[modelKey];
+  if (resolved) {
+    console.log(
+      `[ModelResolver] Resolved model alias: "${modelKey}" -> "${resolved}"`
+    );
+    return resolved;
+  }
+
+  // Unknown model key - use default
+  console.warn(
+    `[ModelResolver] Unknown model key "${modelKey}", using default: "${defaultModel}"`
+  );
+  return defaultModel;
+}
+
+/**
+ * Get the effective model from multiple sources
+ * Priority: explicit model > session model > default
+ *
+ * @param explicitModel - Explicitly provided model (highest priority)
+ * @param sessionModel - Model from session (medium priority)
+ * @param defaultModel - Fallback default model (lowest priority)
+ * @returns Resolved model string
+ */
+export function getEffectiveModel(
+  explicitModel?: string,
+  sessionModel?: string,
+  defaultModel?: string
+): string {
+  return resolveModelString(explicitModel || sessionModel, defaultModel);
+}