Issue #38 (partial): Unicode rename/copy fixes and prompt ownership

[0xeb]

Summary

This PR delivers a partial fix for #38 focused on Unicode rename/copy/paste reliability and prompt ownership behavior.

What is fixed

• Unicode copy-name generation now checks collisions correctly in wide paths.
• Best-fit ANSI fallback detection is enforced before taking ANSI rename/create paths.
• Quick Rename retry flow preserves the latest Unicode value across retries.
• Viewer Ctrl+F "not found" prompts are re-parented to the viewer window.
• Delete prompt default remains intentional (Yes on Enter), with policy centralized.

Known remaining gaps

• Unicode Quick Rename history/dropdown selection still has edge-case rendering/sync issues.
• Follow-up issue: Follow-up: Quick Rename Unicode dropdown selection still degrades text / extension handling #40.

Issue linkage

• Partial for 1.0.1 feedback from testing #38
• Follow-up tracked in Follow-up: Quick Rename Unicode dropdown selection still degrades text / extension handling #40

Validation

• Built locally: cmake --build build --target sally --config Debug
• Manual checks performed for rename/copy/paste and viewer find prompt parenting.