fix(flight): show boundary warning only while flying

design/user-stories/us-004-unlock-and-control-base-flight.md

@@ -21,7 +21,7 @@ As a **player with Base I**, I want to unlock controlled flight around my base s
 - [x] Flight II expands the vertical range to 100 blocks below and above base Y by default.
 - [x] Flight III expands the vertical range to the world's minimum and maximum build heights.
 - [x] A configurable five-block horizontal warning buffer extends beyond the current base radius.
-- [x] Plugin-granted flight remains active in the warning buffer and displays prominent on-screen notice that the player is leaving the base.
+- [x] Plugin-granted flight remains active in the warning buffer, and a prominent on-screen notice that the player is leaving the base appears only while the player is actively flying.
 - [x] Passing beyond the warning buffer removes only flight granted by this plugin.
 - [x] Flight is not granted outside the unlocked vertical range.
 - [x] `/basesettings flight enable` enables unlocked flight idempotently, and `/basesettings flight disable` disables it idempotently.