feat: wire observability into agent loop and MCP server

feat: SQLite metrics store with usage, cost, and tool stats queries

feat: metrics collector aggregates events into SessionEvent

feat: structured logging with JSON file + terminal output

feat: extract LLM usage metrics (tokens, latency) from Ollama response

feat: cost estimator with configurable cloud pricing

feat: observability event dataclasses (LlmCallEvent, ToolEvent, SessionEvent)

docs: observability implementation plan (7 tasks)

docs: observability design spec (logging, metrics, SQLite, cost estimation)

fix: address all code review findings (2 critical + 6 important)

docs: add README with architecture, quick start, and tool reference

feat: MCP server with stdio transport, 7 tools + code_agent

feat: agentic loop with tool execution and max iterations

feat: LLM client with hybrid native/XML tool call parsing

feat: implement all 7 coding tools with auto-registration