fix(qwen): enable Flash-Next multimodal processor paths

[ktsaou]

The release checkpoint reports model_type=qwen3_8_flash_next, but four equivalent Qwen VL processor paths are registered only for its development name, qwen4_exp. The release name therefore misses the established concurrent preprocessing policy, preprocessed-video metadata, timestamp-token construction, and image-only mRoPE fast path.

This adds qwen3_8_flash_next to those four existing allowlists. It changes no algorithms, sampling settings, model weights, or behavior for other model types.

Validation:

• the attested base processor hash matches the recorded production source inventory
• before the patch, the release-name regression has 4 failures while the reference/control cases pass
• after the patch, 4/4 CPU runtime methods pass for worker policy, video metadata/timestamps/embedding slices, and image mRoPE parity
• 84/84 CPU package tests pass
• patch application reconstructs the packaged runtime hash, and the composed 4,392-path source inventory verifies

Known limitation: semantic short-video chronology remains unresolved. Earlier live image cases passed, but observed four-frame videos could still describe events in the wrong order. This PR restores the existing processor path; it does not claim to fix or qualify video ordering.

Validation used a read-only, network-disabled, GPU-disabled container. No image was built, published, or deployed.