feat: Add OpenBao integration for secret management

- Add .env.vault-mapping for LLM API key
- Add .env.example template
- Secret: litellm/master_key for embeddings

Migrated from plaintext .env to OpenBao integration.

Related: OpenBao Phase 4 MCP Servers Integration

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

.env.example

@@ -0,0 +1,9 @@
+# Task MCP Environment Variables
+
+# PostgreSQL connection via pgbouncer
+POSTGRES_HOST=infra.agiliton.internal
+POSTGRES_PORT=6432
+
+# Embedding service configuration
+LLM_API_URL=https://api.agiliton.cloud/llm
+LLM_API_KEY=your_llm_api_key_here