docs: add implementation plan and clarify no-file-loaded errors
Plan artifacts:
- plan.md: Technical context, constitution check, project structure
- research.md: XER format, MCP SDK, SQLite schema decisions
- data-model.md: Entity definitions and database schema
- contracts/mcp-tools.json: MCP tool schemas (9 tools)
- quickstart.md: Usage guide with examples
- CLAUDE.md: Agent context file
Spec updates:
- Add FR-015: NO_FILE_LOADED error requirement
- Add acceptance scenarios for no-file-loaded errors to US3, US4
Bill Ballou
d3474b0f8b