feat(#127): refactor LlmService to use provider pattern

Refactor LlmService to delegate to LlmManagerService instead of using
Ollama directly. This enables multiple provider support and user-specific
provider configuration.

Changes:
- Remove direct Ollama client from LlmService
- Delegate all LLM operations to provider via LlmManagerService
- Update health status to use provider-agnostic interface
- Add PrismaModule to LlmModule for manager service
- Maintain backward compatibility with existing API
- Achieve 89.74% test coverage

Fixes #127

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

apps/api/src/llm/llm.module.ts

@@ -2,8 +2,10 @@ import { Module } from "@nestjs/common";
 import { LlmController } from "./llm.controller";
 import { LlmService } from "./llm.service";
 import { LlmManagerService } from "./llm-manager.service";
+import { PrismaModule } from "../prisma/prisma.module";
 
 @Module({
+  imports: [PrismaModule],
   controllers: [LlmController],
   providers: [LlmService, LlmManagerService],
   exports: [LlmService, LlmManagerService],