LoreKeeper MCP

# Build API Clients ## Why The LoreKeeper MCP server needs API clients to fetch D&D 5e game data from external APIs, but currently has no client implementations, preventing the tools from accessing any game data. ## What Changes - Add async `BaseHttpClient` class with retry logic, rate limiting, and cache integration - Add `Open5eV1Client` for monsters, classes, races, and magic items (3,207+ monsters, 12+ classes, 20+ races, 1,618+ items) - Add `Open5eV2Client` for spells, weapons, armor, backgrounds, feats, and conditions (1,774+ spells, 75 weapons, 25 armor, 54 backgrounds, 91 feats, 21 conditions) - Add `Dnd5eApiClient` for rules and reference data (6 rule categories, 33 rule sections, 8 reference endpoint types) - Add Pydantic response models for data normalization across API versions - Add `ClientFactory` for dependency injection and client instantiation - Add comprehensive error handling with custom exception hierarchy - Add unit and integration tests achieving >90% coverage ## Impact **Affected specs:** - `base-client` (new capability) - `open5e-v1-client` (new capability) - `open5e-v2-client` (new capability) - `dnd5e-api-client` (new capability) **Affected code:** - `src/lorekeeper_mcp/api_clients/` - New directory with base.py, factory.py, open5e_v1.py, open5e_v2.py, dnd5e_api.py - `src/lorekeeper_mcp/api_clients/models/` - New directory with Pydantic response models - `src/lorekeeper_mcp/api_clients/exceptions.py` - New file with custom exceptions - `src/lorekeeper_mcp/cache/db.py` - Integration with existing async cache (no changes needed) - `tests/test_api_clients/` - New test directory with comprehensive test coverage