Add 71 tests covering the entire addon loader pipeline in a new
test_kindred_addon_loader.py file:
- TestAddonState (2): enum members and values
- TestValidVersion (11): _valid_version() regex matching
- TestParseVersionLoader (7): _parse_version() string-to-tuple
- TestAddonRegistry (10): register/get/filter/order/contexts
- TestParseManifest (13): XML parsing, field extraction, validation
errors for bad priority, bad version format, invalid context IDs
- TestValidateDependencies (4): cross-addon dependency checking
- TestValidateManifest (9): version bounds, paths, error accumulation
- TestScanAddons (6): directory walking at depth 1 and 2
- TestResolveLoadOrder (9): topological sort, priority ties, cycle
detection, legacy fallback
Update test runner discovery pattern from 'test_kindred_pure.py' to
'test_kindred_*.py' so both test files are auto-discovered.
All 110 tests pass (71 new + 39 existing).
Refs #396
