fix(files): harden drop operations

[IvanLarinDev]

Summary

• prevent silent auto-sort overwrites by enabling shell rename-on-collision
• avoid unsafe Undo history when destination collisions make results ambiguous
• add config backup, regex timeout, and temp-file virtual extraction safeguards
• add regression tests for the hardened paths

Verification

• dotnet test --nologo
• node hooks/verify.js
• node hooks/design-gate.js --strict