fix(inpaint): normalize cloud masks and reject misaligned inputs

[BerryUIKI]

Inpainting now sends an explicit grayscale edit mask to Fal, validates source/mask dimensions before cache or dispatch for every provider, and preserves painted-region coordinates. Comfy/OpenAI inverse-alpha conversion is vectorized and uses unique temporary files to avoid overlapping-task races. Cache semantics are versioned.

Validation: 16 converter/cloud payload tests and 28 existing creative/upload/cancellation tests passed. Tests inspect a known painted pixel in the actual adapter payload and ensure mismatched dimensions block inference.

• Small implementation/test commit and separate evidence documentation
• Targets dev; required CI must pass
• No secrets, paid inference, or engine mutation

Addresses #106. Keep the issue open: real known-region output preservation remains unverified and needs live engine/provider evidence.