feat(#27): implement intent classification service

Implement intent classification for natural language queries in the brain module.

Features:
- Hybrid classification approach: rule-based (fast, <100ms) with optional LLM fallback
- 10 intent types: query_tasks, query_events, query_projects, create_task, create_event, update_task, update_event, briefing, search, unknown
- Entity extraction: dates, times, priorities, statuses, people
- Pattern-based matching with priority system (higher priority = checked first)
- Optional LLM classification for ambiguous queries
- POST /api/brain/classify endpoint

Implementation:
- IntentClassificationService with classify(), classifyWithRules(), classifyWithLlm(), extractEntities()
- Comprehensive regex patterns for common query types
- Entity extraction for dates, times, priorities, statuses, mentions
- Type-safe interfaces for IntentType, IntentClassification, ExtractedEntity, IntentPattern
- ClassifyIntentDto and IntentClassificationResultDto for API validation
- Integrated with existing LlmService (optional dependency)

Testing:
- 60 comprehensive tests covering all intent types
- Edge cases: empty queries, special characters, case sensitivity, multiple whitespace
- Entity extraction tests with position tracking
- LLM fallback tests with error handling
- 100% test coverage
- All tests passing (60/60)
- TDD approach: tests written first

Quality:
- No explicit any types
- Explicit return types on all functions
- No TypeScript errors
- Build successful
- Follows existing code patterns
- Quality Rails compliance: All lint checks pass

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

apps/api/src/brain/brain.module.ts

@@ -1,17 +1,19 @@
 import { Module } from "@nestjs/common";
 import { BrainController } from "./brain.controller";
 import { BrainService } from "./brain.service";
+import { IntentClassificationService } from "./intent-classification.service";
 import { PrismaModule } from "../prisma/prisma.module";
 import { AuthModule } from "../auth/auth.module";
+import { LlmModule } from "../llm/llm.module";
 
 /**
  * Brain module
  * Provides unified query interface for agents to access workspace data
  */
 @Module({
-  imports: [PrismaModule, AuthModule],
+  imports: [PrismaModule, AuthModule, LlmModule],
   controllers: [BrainController],
-  providers: [BrainService],
-  exports: [BrainService],
+  providers: [BrainService, IntentClassificationService],
+  exports: [BrainService, IntentClassificationService],
 })
 export class BrainModule {}