fix: application controller avoid missing requested app operations

[drewbailey]

Under API server pressure, an Application update that adds .operation
can reach the controller at an awkward time: refresh processing may
enqueue the operation queue before the informer cache reflects the new
operation, and processAppOperationQueueItem() previously only performed
a live GET when informer state already showed app.Operation != nil. In
that case the worker could observe a stale Application, treat it as
having no requested operation, and silently return. The operation would
only start later if some other refresh or comparison-expiry path
re-enqueued the app after informer state caught up.

Address that gap by tracking explicit operation requests when an
Application update transitions from operation=nil to operation!=nil,
enqueueing the operation queue immediately, and allowing operation
workers to do a live GET whenever that explicit request marker is
present even if informer state is stale. Retry transient GET failures
such as timeout, 429, or 503 instead of dropping the request.

Add regression coverage for immediate operation enqueueing, recovery
from stale informer state, and requeue behavior on transient live-GET
failures.

Checklist:

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• The title of the PR conforms to the Title of the PR
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• Does this PR require documentation updates?
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[codecov]

Codecov Report

❌ Patch coverage is 82.50000% with 7 lines in your changes missing coverage. Please review.
✅ Project coverage is 63.35%. Comparing base (62670d6) to head (d666629).

Files with missing lines	Patch %	Lines
controller/appcontroller.go	82.50%	6 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #27133      +/-   ##
==========================================
+ Coverage   63.33%   63.35%   +0.01%     
==========================================
  Files         415      415              
  Lines       56545    56584      +39     
==========================================
+ Hits        35815    35849      +34     
- Misses      17350    17355       +5     
  Partials     3380     3380              

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