Implement TerminologyRepository with Supabase fetch

Use a sealed class or freezed union for TerminologyFailure (e.g. networkError, cacheEmpty, parseError, authError) so callers are forced to handle all cases via exhaustive switch. Prefer fpdart's Either> as the return type for consistency with functional Dart patterns; if the team has not adopted fpdart, a simple Result custom class is acceptable but must be documented. The Supabase call should be: `await _supabase.from('organization_configs').select('labels').eq('org_id', orgId).single()`.

Wrap the entire method body in a try-catch that catches Object (not just Exception) to guarantee no leakage. Do not use `maybeSingle()` unless the schema guarantees at most one row — use `.single()` and map the empty-result exception to an empty map. Inject dependencies via constructor so the class is testable without a live Supabase instance.

Unit tests must mock both SupabaseClient and TerminologyCacheAdapter. Cover: (1) successful fetch → cache write → returns Right(labelMap); (2) network exception → cache hit → returns Right(cachedMap); (3) network exception → cache miss → returns Left(networkAndCacheEmpty); (4) Supabase returns null labels → treated as empty map, cached, returned as Right({}); (5) Supabase returns malformed JSON → mapped to Left(TerminologyFailure.parseError). Use flutter_test with mockito or mocktail. Minimum 90% branch coverage on the repository class.