feat(domain): WordCounterService + WordCountResult + ChargeableCharConfig entity + exceptions (PRC-001)

- WordCounterService: pure domain service, 7-step algorithm (null/empty fast path → length check → emoji detection via Rune.EnumerateRunes → count specials before replace → replace specials+hyphens → collapse whitespace → tokenize)
- WordCountResult: sealed record with TotalWords + IReadOnlyDictionary<string,int> SpecialCharCounts
- 4 domain exceptions extending DomainException: EmojiDetectedException, WordCountValidationException, ChargeableCharConfigInvalidException, ChargeableCharConfigForwardOnlyException
- ChargeableCharConfig: rich entity with Create factory (invariants), Rehydrate reconstructor, ScheduleNewPrice (forward-only, returns new entity), Deactivate (idempotent)
- ChargeableCharCategories: enum-as-string constants (Currency, Percentage, Exclamation, Question, Other)
- DomainTimeProviderExtensions: internal GetArgentinaToday helper (mirrors Application.Common without creating Domain→Application dependency)
- 60 new tests: 25 golden cases all GREEN, 12 entity invariant tests, 12 exception tests, 5 WordCountResult tests, 6 ChargeableCharConfig entity tests

src/api/SIGCM2.Domain/Pricing/WordCounter/WordCountResult.cs

@@ -0,0 +1,10 @@
+namespace SIGCM2.Domain.Pricing.WordCounter;
+
+/// <summary>
+/// PRC-001 — Immutable value object representing the result of a word count operation.
+/// TotalWords: number of whitespace-separated tokens after normalization.
+/// SpecialCharCounts: map of category name → occurrence count in the ORIGINAL (pre-normalization) text.
+/// </summary>
+public sealed record WordCountResult(
+    int TotalWords,
+    IReadOnlyDictionary<string, int> SpecialCharCounts);