[AZ-1126] Migrate capturedAt to DateTimeOffset

Co-authored-by: Cursor <cursoragent@cursor.com>

_docs/03_implementation/implementation_completeness_cycle13_report.md

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+# Product Implementation Completeness — Cycle 13
+
+**Date**: 2026-06-26
+**Cycle**: 13
+
+## Per-Task Classification
+
+| Task | Verdict | Evidence |
+|------|---------|----------|
+| AZ-1126 | PASS | `UavTileMetadata.CapturedAt` is `DateTimeOffset` with `UtcOffsetRequiredDateTimeOffsetConverter`; validator, quality gate, and upload handler compare via `UtcDateTime`; contract patched to 1.2.1; integration + unit tests green |
+
+## System Pipeline Audit
+
+No new end-to-end pipelines introduced. UAV upload pipeline remains WIRED (filter → handler → quality gate → repository).
+
+## Gate Verdict: PASS