feat: NOTAM client + parser (M5a)

[tomassasovsky]

Summary

• Adds NotamParser (zones_api_client): parses EANA's POST /notam/pib HTML table into time-bounded ZoneData — Desde:/Hasta: validity (UTC), COORD GEO DMS polygons, single-coordinate + RDO <n>NM circles, and vertical limits (GND, <n>FT AGL, FL<n>). source = notam with activeFrom/activeTo.
• Tolerant by design: a NOTAM with no derivable geometry (point-only obstacle, VOR outage, airway-only reference) is surfaced in ungeocodable for review, never silently dropped.
• Adds NotamClient: fetches per FIR code (-EF -CF -VF -MF -RR) via the site's session-cookie + AJAX-header flow (reverse-engineered from the live endpoint); fetchAllFirs merges and tolerates a single-FIR outage.

Plan

feat: complete, authoritative airspace zone coverage — Milestone M5a (data layer; standalone, not wired into ingest — that's M5b). Depends on M1's validity fields.

Test plan

• zones_api_client: dart test — parser tested against a real captured EANA fixture (test/fixtures/notam_ef_sample.html: 1 polygon, 2 circles, 2 un-geocodable). Asserts DMS→lat/lon, RDO→radius, FL/AGL limits, and UTC validity windows.
• Mocked-HTTP client flow: session GET → POST indicador → parse; non-200 throws NotamException; fetchAllFirs skips a failing FIR.
• dart analyze + dart format clean.

Notes

• The fixture is a small real sample captured from EANA's public reference endpoint, used only to test the parser. EANA's page is reference-only with no published reuse license — M6 confirms attribution/terms and the data-sources page entry; this PR does not present it as an official PIB.
• Base branch is feat/zone-provenance-validity-fields (M1). Endpoint is an undocumented scrape (HTML shape can change) — parsing is fixture-tested and tolerant per the plan's risk note.

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