feat: agent routing engine — cost/capability matrix (P2-003)

Add RoutingService that selects optimal LLM model based on task type,
cost tier, capability requirements (reasoning, image, context window),
and provider preference. Scoring algorithm ranks all available models.

- RoutingService: route() for best match, rank() for scored list
- POST /api/providers/route and /api/providers/rank endpoints
- Routing types in @mosaic/types (CostTier, TaskType, RoutingCriteria)
- Cost tier classification: cheap (<$1/M), standard (<$10/M), premium

Closes #21

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

packages/types/src/index.ts

@@ -3,3 +3,4 @@ export const VERSION = '0.0.0';
 export * from './chat/index.js';
 export * from './agent/index.js';
 export * from './provider/index.js';
+export * from './routing/index.js';

packages/types/src/routing/index.ts

@@ -0,0 +1,25 @@
+/** Cost tier for model selection */
+export type CostTier = 'cheap' | 'standard' | 'premium';
+
+/** Task type hint for routing */
+export type TaskType = 'chat' | 'coding' | 'analysis' | 'summarization' | 'general';
+
+/** Routing criteria for model selection */
+export interface RoutingCriteria {
+  taskType?: TaskType;
+  costTier?: CostTier;
+  requireReasoning?: boolean;
+  requireImageInput?: boolean;
+  minContextWindow?: number;
+  preferredProvider?: string;
+  preferredModel?: string;
+}
+
+/** Result of a routing decision */
+export interface RoutingResult {
+  provider: string;
+  modelId: string;
+  modelName: string;
+  score: number;
+  reasoning: string;
+}