feat(server): inference state-graph + supervisor, memory tools, MCP client, schema, routes
- Add state-graph.ts: typed state machine for inference lifecycle
- Add supervisor.ts: agent supervisor pattern for multi-agent coordination
- Add export-formatter.ts: structured export formatting
- Add manage_memory.ts: memory CRUD tool for agent persistence
- Add get_wiki_article.ts: codecontext wiki article retrieval
- Extend memory/index.ts: 3-tier memory (context/daily/core)
- Extend MCP client: mcp-config.ts env-var substitution
- Update schema.sql: agent_sessions, tasks, pending_changes extensions
- Update API types: MessageMetadata, ErrorReason, AgentSessionConfig
- Update routes: chats, messages, sessions — column renames and agent_session_id
- Update inference: error handler, payload builder, stream phase, turn orchestrator