Resolve org-specific activity type labels via provider

Add resolvedLabel as a nullable late field or include it in copyWith/fromJson as an optional parameter defaulting to null. The cleanest pattern is to add a withResolvedLabel(String label) method on ActivityType that returns a copyWith-constructed instance with the label set, keeping the domain model pure. In the service, after fetching from cache/repository, resolve labels in a single pass: final labelMap = await labelsProvider.getTerminologyMap(orgId); return types.map((t) => t.withResolvedLabel(labelMap[t.labelKey] ?? t.labelKey)).toList().

The OrganizationLabelsProvider should already be a Riverpod provider — inject it into ActivityTypeService via constructor parameter typed as OrganizationLabelsProvider (or its interface). Ensure this integration does not break existing callers of getActiveTypes — resolvedLabel being populated is additive, not breaking.

Unit tests using flutter_test with mocked OrganizationLabelsProvider: (1) known labelKey resolves to org-specific display string, (2) unknown labelKey falls back to raw labelKey without error, (3) empty terminology map results in all types using labelKey as resolvedLabel, (4) provider injection: service calls OrganizationLabelsProvider.getLabel(orgId, labelKey) not a static method, (5) toJson() output does not include resolvedLabel key, (6) fromJson() creates ActivityType with resolvedLabel as null until service resolves it. Verify OrganizationLabelsProvider is called exactly once per getActiveTypes invocation (not once per activity type) using mockito verify call count.