feat: cross-source AIP+OpenAIP zone merge (M2)

[tomassasovsky]

Summary

• Adds ZoneMerger.merge (zones_api_client): when an OpenAIP zone and an ANAC AIP zone share a ZoneIdentity.matchKey, they collapse into one zone — OpenAIP vertex-exact geometry carrying AIP authority (category, permissions, vertical limits), source = openaip + confirmedBy = aip.
• Both the runtime ZoneDeduplicator and the backend ZoneIngestService delegate to the single merge function, so the rule lives in exactly one place (no duplicated merge logic across layers).
• Safety-first: a matchKey miss keeps both zones (a double-render beats dropping an authoritative zone); the OpenAIP candidate carrying a real polygon is preferred for geometry.

Plan

feat: complete, authoritative airspace zone coverage — Milestone M2 (depends on M1).

Test plan

• zones_api_client: dart test — incl. zone_merger_test.dart (EZE/Aeroparque/SAR collapse → one zone each, polygon preference, keep-both on miss, keyless passthrough) and the designator-collision guard in zone_identity_test.dart (SAR 01–85 + distinct CTR/TMA names never share a matchKey).
• flight_rules_repository: dart test — dedup now runs id-collapse → cross-source merge; all existing tests green.
• dart analyze + dart format clean on changed files.
• Reviewer: spot-check a real ingest run once OpenAIP + AIP both have live data (M3b) — confirm EZE/Aeroparque render once.

Notes

• Base branch is feat/zone-provenance-validity-fields (M1) since M2 builds on the typed source/confirmedBy fields. Merge M1 first.
• Residual geographic overlaps (genuinely distinct zones, not matchKey pairs) keep deterministic ordering via the existing MapZoneDisplay severity sort; no separate stacking rule was needed.

🤖 Generated with Claude Code