Fix Windows embedding runtime self-heal

[ganisback]

Summary

• Avoid installing torchaudio for the Windows embedding runtime and auto-remove broken existing torchaudio installs.
• Verify Windows embedding readiness with real torch/transformers imports so bad runtimes self-heal instead of starting a broken worker.
• Persist embedding and Diffusers worker logs and include the output tail in startup errors.

Fixes #54

Test plan

• go test ./internal/imagegen ./internal/embedding ./internal/server ./internal/config ./internal/logutil

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