Unable to assign atom as a leaving group event if it is eligable

[AlexeyGirin]

CONFIRMED BY @ljubica-milovic

Steps to Reproduce

1. Open Molecules mode (clean canvas)
2. Load structure from clipboard: CC%91C(C)C(C)C(C)C(C)C(C)C.[*:1]%91 |$;;;;;;;;;;;;;_R1$|

3. Select whole structure

4. Press Create monomer button
5. Select any atom eligible for LGA (every atom that has one and only one simple-single bond to another atom in the structure, and is not already an LGA.)

6. Call context menu

Actual behavior
System opens context menu with no Assign as a leaving group option

Expected behavior
System opens context menu with Assign as a leaving group option

As per requirement:

3.2. Users can set a new AP by:

3.2.1. R-clicking on a potential LGA (option "Make a leaving group atom"), and choosing an R-number for that AP.

3.2.1.1. Potential LGA is every atom that has one and only one simple-single bond to another atom in the structure, and is not already an LGA.

Environment details:

• Ketcher Version 3.8.0-rc.2 Build at 2025-09-05; 20:35:42
• Indigo Version 1.36.0-rc.2.0-ge0390621c-wasm32-wasm-clang-19.0.0
• Chrome Version 140.0.7339.81 (Official Build) (64-bit)
• Win10

Found while testing: #7441