Make TTS voice renames rollback-safe

[Blackspirits]

Summary

The new TTS Voice Manager renames a file-backed clone by moving its sidecars first and its WAV last. Two failure modes can corrupt or destroy voice data:

• on case-sensitive file systems, names that differ only by case are treated as the same file and moved with overwrite:true, so renaming CaseVoice to caseVoice can overwrite an existing distinct voice;
• if a sidecar/WAV move fails after earlier files have already moved, the voice can be left split across old and new base names with no rollback.

This change:

• stages the WAV and all matching sidecars under unique temporary names before publishing any destination
• checks all destination paths only after staging, which makes case-only renames portable across case-sensitive and case-insensitive file systems
• never uses overwrite semantics for a rename destination
• rolls back staged/published files in reverse order on failure
• moves published case-only paths through a temporary file during rollback so original casing can be restored reliably
• keeps enumeration/staging errors inside the existing error return contract
• makes prepared-cache cleanup best-effort so cache deletion cannot roll back an otherwise successful voice rename
• preserves the existing name validation, non-file voice restrictions, delete behavior and logging

Regression coverage

• successful WAV + transcript rename still moves sidecars and drops the prepared cache
• an existing target voice is still refused
• a target-sidecar collision leaves WAV and all source sidecars unchanged and leaves no staging files
• a case-only rename succeeds when there is no distinct target
• on a case-sensitive file system, a distinct target differing only by case is preserved rather than overwritten
• existing invalid-name/delete/non-file tests remain in place

Validation

• diff is limited to VoiceFileRename.cs and VoiceFileRenameTests.cs
• upstream later advanced from the review base to 9c0f6bdd77bc12bafff66f748b97c8b3d3a2d5b7; the intervening commits only update Turkish.json and do not touch the TTS Voice Manager rename path
• full solution restore passed
• full solution build passed
• full solution test suite passed on the first run
• retry step was not used
• validation run: #34760867384

Base is upstream 4771a22765acdbdf5bd5b8a1c02f378c15e73ac9.

AI assistance: ChatGPT was used to adversarially review the newly introduced Voice Manager file-rename flow, identify cross-platform overwrite and partial-move failure modes, design rollback-safe staging, and add focused regressions.

[Blackspirits]

Independent adversarial re-check: the final diff remains limited to the rename helper and focused regression tests. Source files are staged before destination checks, no destination uses overwrite semantics, partial staging/publishing paths attempt reverse-order rollback, case-only renames are handled without destroying a distinct case-sensitive target, and cache cleanup is intentionally best-effort after the rename transaction. Full CI run #34760867384 passed restore/build/full tests on the first run with no retry. No blocker identified. Keep draft; no merge/promotion performed.