Person: explicit id, Modify/decidability, wire up dateOfBirth/dateOfDeath

[DutchJaFO]

Background

Person has no explicit-id schema section today — it's discovered only implicitly via a Quote's author string field, matched by natural key (name) via ResolvePersonAsync, and is Add-only (EnsurePersonExistsAsync is a plain insert-if-not-exists). Person is already a global entity (no SourceId — unlike Character, one "Winston Churchill" row is already shared across every quote that references him), which makes it the simplest of the remaining entities to give explicit-id/Modify support to: no linkage/scoping design question, unlike Character. This issue also wires up Person.DateOfBirth/DateOfDeath — both columns already exist on the entity (predating this milestone) but nothing anywhere sets them; the Modify plumbing this issue adds makes populating them nearly free, and leaving them permanently dead is its own latent gap otherwise.

This issue's "global entity, Name-keyed" Modify shape is deliberately meant to be the direct template for Character's own explicit-id/Modify issue, once Character's separate per-Source-to-global identity migration (see the linked follow-on issue) lands.

What needs to be done

1. schemas/source-extended.schema.json gains a people array section + person $def: id (required, UUID v4 pattern, same regex as source/stageDirection/etc.), name (required), dateOfBirth (optional, imprecise ISO 8601 string, same convention as SourceEntry.Date), dateOfDeath (optional, same convention). Purely additive — a file without a people section parses identically to today.
2. New PersonEntry.cs record in Quotinator.Core.Import, doc-commented like SourceEntry. ParsedSourceFile gains People (defaults []). SourceQuoteFileReader.TryParseExtended gains the new root-key parse.
3. Sql.People (src/Quotinator.Engine/Queries/Sql.cs) gains SelectExistingById (returns Name, DateOfBirth, DateOfDeath, CompletenessStatus), UpdateFieldsById, SelectCompletenessById, UpdateCompletenessById.
4. New PlanPeopleAsync (src/Quotinator.Engine/Database/ImportActionPlanner.cs), run before the quote loop, mirroring PlanSourcesAsync's shape: id-match lookup → field-map diff (name, dateOfBirth, dateOfDeath) → unchanged-check (silent reuse) → policy-based resolution → CompletenessGuard.ShouldBlock evaluated against the policy-resolved value → stage Blocked or Modify. Falls back to the existing natural-key lookup (Sql.People.SelectIdByName) when no id match — a not-yet-declared-by-id row found this way stays Add-only/natural-key-matched, same scope boundary as Source's own natural-key fallback. A person discovered only implicitly through a Quote's author string (no explicit people[] entry) stays Add-only forever, same rule.
5. ApplyResolvedActionAsync's Person case splits on ActionType: Add unchanged; Modify calls the new Sql.People.UpdateFieldsById against MergedFields — the first write path that ever populates DateOfBirth/DateOfDeath.
6. DecideAsync gains an EntityType == Person && ActionType == Modify branch, mirroring Source's branch shape.
7. ComputeAmbiguousFields gains a Person case.
8. ReverseAppliedActionsAsync's Person case splits on ActionType: Add keeps today's soft-delete-if-unreferenced; Modify restores Name/DateOfBirth/DateOfDeath via UpdateFieldsById from ExistingValue.
9. ClearStaleAddTargetsAsync's Person cleanup branch currently uses the Guid-typed repository path (_personRepository.HardDeleteAsync(Guid.Parse(...))), correct today only because every Person id is EntityIdentity-derived (always uppercase). This issue must switch it to the raw-SQL, case-preserving pattern (RepositorySql.HardDelete("People")), the same fix Source: explicit file-carried id, decoupling matching from Title/Type/Date content #162 made for Source — an explicit people[] id is file-authored and not guaranteed uppercase. Non-optional part of this issue's scope, not a nice-to-have.
10. ConflictDecisionRequest gains PersonName, PersonDateOfBirth, PersonDateOfDeath (nullable FieldDecision?).

Expected tests

Test class	Test method	Starts
New: Quotinator.Core.Tests	SourceQuoteFileReader_PeopleSection_ParsesCorrectly	❌
New: Quotinator.Engine.Tests	PlanPeopleAsync_IdMatchFound_NameDiffers_StagesModifyAction	❌
New: Quotinator.Engine.Tests	PlanPeopleAsync_IdMatchFound_NothingChanged_NoActionStaged	❌
New: Quotinator.Engine.Tests	PlanPeopleAsync_NoIdMatch_FallsBackToNaturalKey_NoActionStaged	❌
New: Quotinator.Engine.Tests	PlanPeopleAsync_CompleteStatus_StagesBlockedNotModify	❌
New: Quotinator.Engine.Tests	PlanPeopleAsync_CompleteStatus_SkipPolicy_DoesNotBlock	❌
New: Quotinator.Engine.Tests	ApplyBatchAsync_PersonModify_WritesDateOfBirthAndDateOfDeath	❌
New: Quotinator.Engine.Tests	DecideAsync_PersonModify_ResolvesFieldDecisions	❌
New: Quotinator.Engine.Tests	ReverseBatchAsync_PersonModify_RestoresExistingValue	❌
New: Quotinator.Engine.Tests	ClearStaleAddTargetsAsync_PersonExplicitLowercaseId_HardDeletesCorrectly	❌

Definition of done

• All expected tests listed above start red before implementation
• All requirements implemented
• All expected tests pass (green)
• No regression in related tests
• Findings summarised in a closing comment