Triage: complete kit webhook dedup migration (#241) and fix RN-IAP Android disconnect (#408)

[hyochan]

• kit: fold webhook dedup into webhookEvents and drop webhookIdempotencyKeys (staged migration) #241 kit webhookIdempotencyKeys drain window elapsed (started 2026-08-07). Confirm production zero rows, then ship phase 4 (drop table, legacy fallbacks, key-specific prune/cascades). Keep webhookEvents retention cron.
• Android: react-native-iap never learns about a billing service disconnect, and reconnect() cannot recover #408 Android react-native-iap: billing service disconnect leaves isInitialized true so reconnect() is a no-op and connected stays lied. Add connection-state listener (or clear flag on disconnect) so initConnection rebuilds. Open since 2026-08-30, no comments.
• Alternative Billing Only: dedicated 3-step APIs throw SERVICE_DISCONNECTED (-1), and the documented replacement (external-offer) is a different Play program requiring an external link #364 Alternative Billing Only: waiting on reporter for current Play Console enrollment program after doc fix in ci: skip native matrices for docs-only changes #363.
• [godot-iap] Avoid repeated Windows editor errors for Apple-only GDExtension #366 (closed) recent Mac freeze note from reporter; short recovery already acknowledged, no reopen unless it worsens.

[hyochan]

Closing as redundant. Every item here already has its own issue: #241, #408, and #364 are open and current, and #366 is closed. A summary issue adds a second place to keep up to date without adding information — track the work in the individual issues.