fix(PlanView): reload mission item editors from tree root to avoid stale-delegate loads

[DonLakeFlyer]

Problem

PlanViewLayerUITest fails intermittently in CI (most recently on #14667) with strict-mode log failures:

QQmlContext: Cannot set context object on invalid context.
QQmlComponent: Cannot create a component in an invalid context

This is the CI-only "invalid context" flavor noted as unresolved in #14638 ("never reproduced locally in ~340 runs... if it recurs in CI after this change it can be hunted separately"). It recurred.

Root cause

MissionItemEditor.qml used a Connections { target: missionItem } to reload its editor Loader on isCurrentItemChanged. TreeView (with reuseItems: false) releases delegates by invalidating their QML context immediately while deferring actual destruction via deleteLater. In that window the Connections to the persistent MissionItem C++ object still fires, and Loader.setSource() attempts a component load in the invalidated context. QQuickLoaderPrivate::_q_sourceLoaded() then does new QQmlContext(creationContext) + setContextObject() on the dead context — producing exactly the two warnings above.

The race needs delegate teardown (layer switch / group collapse / forceLayout) to coincide with a current-item change — e.g. the takeoff-item insertion in test step 2.2 — and is far more likely on slow CI runners, which is why it never reproduced locally.

Fix

Invert the control:

• Remove the per-delegate Connections from MissionItemEditor.qml; rename _loadEditor() to public reloadEditor().
• PlanTreeView.qml (whose root outlives all delegates) reacts to MissionController::planViewStateChanged — emitted whenever the current plan-view item changes — and calls reloadEditor() only on delegates that are still live, via itemAtCell() over the visible rows. Released delegates are unreachable through itemAtCell, so no load can ever be triggered in an invalidated context.
• Newly created delegates still load their editor from Component.onCompleted.

Testing

• 100 consecutive local runs of PlanViewLayerUITest with the fix (30 direct binary + 70 via ctest): 0 failures.
• PlanViewUITest and ToolbarIndicatorUITest pass (editor expand/collapse regression check).
• Note: the invalid-context flavor only ever reproduced in CI, so CI is the real verifier here.

[Copilot]

Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated no new comments.

[github-actions]

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