docs: add specification and implementation plan for direct database access feature

This feature (002-direct-db-access) enables scripts to query schedule data
directly via SQL after loading XER files through MCP. Key additions:

- spec.md: Feature specification with 3 user stories
- plan.md: Implementation plan with constitution check
- research.md: Technology decisions (SQLite file, WAL mode, atomic writes)
- data-model.md: DatabaseInfo, SchemaInfo, TableInfo entities
- contracts/mcp-tools.json: Extended load_xer schema, new get_database_info tool
- quickstart.md: Usage examples for direct database access
- tasks.md: 16 implementation tasks across 6 phases

specs/002-direct-db-access/checklists/requirements.md

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+# Specification Quality Checklist: Direct Database Access for Scripts
+
+**Purpose**: Validate specification completeness and quality before proceeding to planning
+**Created**: 2026-01-08
+**Feature**: [spec.md](../spec.md)
+
+## Content Quality
+
+- [x] No implementation details (languages, frameworks, APIs)
+- [x] Focused on user value and business needs
+- [x] Written for non-technical stakeholders
+- [x] All mandatory sections completed
+
+## Requirement Completeness
+
+- [x] No [NEEDS CLARIFICATION] markers remain
+- [x] Requirements are testable and unambiguous
+- [x] Success criteria are measurable
+- [x] Success criteria are technology-agnostic (no implementation details)
+- [x] All acceptance scenarios are defined
+- [x] Edge cases are identified
+- [x] Scope is clearly bounded
+- [x] Dependencies and assumptions identified
+
+## Feature Readiness
+
+- [x] All functional requirements have clear acceptance criteria
+- [x] User scenarios cover primary flows
+- [x] Feature meets measurable outcomes defined in Success Criteria
+- [x] No implementation details leak into specification
+
+## Notes
+
+- All items pass validation
+- Spec is ready for `/speckit.clarify` or `/speckit.plan`
+- The feature cleanly extends existing functionality (load_xer) with persistent database output
+- Assumptions section documents reasonable defaults for database location and persistence behavior