Support for stereo-flags in macromolecules mode

[Copilot]

How the feature works? / How did you fix the issue?

Adds stereo-flag rendering (ABS, AND Enantiomer, OR Enantiomer, Mixed) in macromolecules mode. Stereo flags visible in molecules mode are now preserved and displayed when switching to macromolecules mode.

Core changes:

• CoreStereoFlag entity: stores position, flag type, and linked monomer reference
• StereoFlagRenderer: renders flag labels with hover/selection support
• StereoFlagAddOperation / StereoFlagDeleteOperation: undo/redo support
• MacromoleculesConverter: creates stereo flags from fragment enhancedStereoFlag during conversion
• DrawingEntitiesManager: manages stereo flag lifecycle and auto-syncs selection with parent monomer

Behavior:

• Selecting a molecule auto-selects its stereo flag
• Stereo flags can be moved independently of their molecule
• Moving a molecule does not automatically move its stereo flag (per requirement)

Check list

• unit-tests written
• e2e-tests written
• documentation updated
• PR name follows the pattern #1234 – issue name
• branch name doesn't contain '#'
• PR is linked with the issue
• base branch (master or release/xx) is correct
• task status changed to "Code review"
• reviewers are notified about the pull request

Original prompt

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This section details on the original issue you should resolve

<issue_title>Support for stereo-flags in macromolecules mode</issue_title>
<issue_description>Background

[This is a part of the larger story about transferring all molecules functionality to macromolecules mode.]

Currently we have stereo-flags implemented in Molecules mode and we need to support the same functionality at Macromolecules mode

Requirements
Stereo flags are the following labels appears near molecule that have stereo-isometric: ABS, AND Enantiomer, OR Enantiomer and Mixed:

1. If a stereo-flag is visible in small molecules mode canvas it should be visible in macromolecules mode canvas.

2. If a molecule with whom the stereo-flag is associated gets selected (on macromolecules mode canvas) the stereo-flag should also get selected.

3. The users should be able to move the stereo-flags independent of the molecule, but not the opposite.</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Support for stereo-flags in macromolecules mode #6918

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