#2040: Fix workspace ComboBox reset on project switch

[KarimALotfy]

This PR fixes #2040

Implemented changes:

• Workspace onAction was re-registered inside setWorkspaceComboBox()
  on every project selection. Clearing the items mid-setup fired the old
  handler with a stale/null workspace, causing a FileNotFoundException
  error dialog or a NullPointerException that aborted addAll().
• Handler is now registered once in initialize() via this::onWorkspaceSelected.

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Testing instructions

• Open GUI by running AppLauncher
• Select a project → workspace dropdown populates, prompt text shown
• Switch to a different project → workspace resets to prompt text, buttons re-disabled
• Select a workspace in new project → no error dialog, correct context

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Checklist for this PR

Make sure everything is checked before merging this PR. For further info please also see
our DoD.

• When running mvn clean test locally all tests pass and build is successful
• PR title is of the form #«issue-id»: «brief summary» (e.g. #921: fixed setup.bat). If no issue ID exists, title only.
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  with internal
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[coveralls]

Coverage Report for CI Build 28436052186

Coverage increased (+0.01%) to 71.372%

Details

• Coverage increased (+0.01%) from the base build.
• Patch coverage: No coverable lines changed in this PR.
• 21 coverage regressions across 2 files.

Uncovered Changes

No uncovered changes found.

Coverage Regressions

21 previously-covered lines in 2 files lost coverage.

File	Lines Losing Coverage	Coverage
com/devonfw/ide/gui/MainController.java	20	65.63%
com/devonfw/tools/ide/tool/ide/IdeToolCommandlet.java	1	78.33%

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Coverage Stats

Relevant Lines:	16283
Covered Lines:	12119
Line Coverage:	74.43%
Relevant Branches:	7288
Covered Branches:	4704
Branch Coverage:	64.54%
Branches in Coverage %:	Yes
Coverage Strength:	3.15 hits per line

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💛 - Coveralls