YachtMemory Phase 1C.1c v1 - revision-aware Stay enrichment
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Basis
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Full replacement of the uploaded, validated Phase 1B v1.1
src/services/StayEnrichmentWriter.php.

Changes
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- Reads the authoritative current revision from yachtmemory_derived.stays.
- Reads stay_enrichment.stay_revision with existing enrichment values.
- INSERT stores the current Stay revision.
- Revision mismatch forces UPDATE, even if rounded enrichment values are identical.
- UPDATE stores both current enrichment values and current Stay revision.
- Equal revision + equal values remains UNCHANGED and performs no write.
- Existing Phase 1B telemetry flattening and 3-decimal comparison semantics are retained.

No SQL migration is included. Phase 1C.1a already created stay_enrichment.stay_revision.

Test
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Syntax first:
  php -l src/services/StayEnrichmentWriter.php
  php -l shared_dashboard/scripts/test_stay_enrichment_revision.php

Dry run:
  php shared_dashboard/scripts/test_stay_enrichment_revision.php 1

Expected current real state:
  Stay #1-35: UNCHANGED, enrichment rev 1 -> 1
  Stay #36:   UPDATE,    enrichment rev 1 -> 2
  INSERT 0 | UPDATE 1 | UNCHANGED 35

Do not use --apply until the dry-run output has been reviewed.