docs: trim comments to non-obvious WHY only

[erikfrerejean]

Summary

Reviewed every comment in src/ against the eight ADRs, deptrac.yaml, and the Igor worker-safety check (ADR-0007), applying a strict WHY-only standard: a comment earns its place only if it carries non-obvious rationale not already documented elsewhere.

• Removed docblocks that merely restated the type name/shape (WHAT) or duplicated a governing ADR: AuditEvent, Changeset, FieldChange, RenderLine, RenderPayload, Subject, AuditActor, AuditEntry, AuditPage, AuditRecord, Actor, DefaultRecorder, IdentityGenerator, Origin, RecordStore, Recorder.
• Trimmed ADR/tooling-restating clauses, keeping the non-obvious residue:
  • ActorResolver / OriginResolver — dropped the "live, at call time (worker mode)" clauses (ADR-0007 + Igor CI).
  • SubjectLabeller — kept the snapshot-survives-deletion WHY, dropped the redundant null-return note.
  • AbstractAuditEvent — kept the extension-seam guidance, dropped the ADR-0002 "frozen render payload" echo.
  • AuditQuery — kept "filters combine with AND" (non-obvious), dropped the name restatement.
  • RecordReader — kept the actors()-for-filter-lists rationale.
  • NewAuditRecord — kept the write-input vs Record\AuditRecord disambiguation.

All @param/@return/@var type annotations preserved (PHPStan needs them).

Note

With strict WHY-only, the central domain interfaces (AuditEvent, Recorder, AuditRecord) now carry no class-level orientation — that context lives in the ADRs. If this hurts source-level discoverability for consumers, a one-line role on public types is the middle ground.

Test plan

• composer cs-check — clean
• composer phpstan — 0 errors
• composer test — 18 tests, 51 assertions pass