RNA Builder: Monomers remain grayed out after canceling preset creation

[MarinaKisacik]

Found while testing #9120
Steps to Reproduce:

1. Switch to Macro mode
2. Expand the RNA builder in the RNA tab of the Monomer library
3. Select a particular sugar, for instance, dier
4. Observe bases and phosphates -> some of them are grayed out (according to the preset creation logic)
5. Click Cancel button in the RNA builder
6. Observe bases and phosphates again

Actual Results
Grayed-out bases and phosphates remain unavailable even after canceling the RNA builder

Bases.and.phosphate.remain.grayed.out.mp4

Expected Result:
All bases and phosphates should return to their available (enabled) state after the RNA builder is canceled

Found in Environment:

• Ketcher Version 3.15.0-rc.1 Build at 2026-04-02; 15:41:30
• Indigo Version 1.43.0-rc.1.0-gd74653443-wasm32-wasm-clang-19.0.0
• Chrome Version 146.0.7680.178 (Official Build) (64-bit)
• Win11

Reproducible in Ketcher Version 3.12.0 Build at 2026-03-04; 11:27:49