Airport Intelligence stage D2–D5: runway, approach, context and release guards

[Boym323]

Stage D2–D5 (follows merged D1 #629)

• D2: confidence-gated interpretation of per-flight deduplicated 15-minute observed runway windows vs readiness-gated PUBLIC runway prediction; observed transition is different from predicted divergence and uncertain evidence stays UNKNOWN.
• D3: bounded per-aircraft approach evidence: corroborated holding, go-around, approach and same-flight re-approach, with strict time, identity and completeness checks; no inferred landing.
• D4: source-labeled explanation combining existing runway/prediction, METAR/wind, approach exceptions and bounded flow data; link to existing ATC explorer. Explicit NO_ATC_CLEARANCE_EVIDENCE; never claim an ATC instruction.
• D5: unit, ambiguous/stale/scarce-evidence regressions, single-stream/bounded/no-auto-PUBLIC release boundary, synced EN+CS docs, bilingual UI.

No new API routes, DB changes, providers, pollers, SSE subscribers, persistence or automatic PUBLIC graduation. D1 #629 is already in main. Await PR CI/CodeQL; merge only after green; verify main Release validation + Deploy production.