Add OpenVINO export support for FLUX.2-dev / Flux2Pipeline

I’m trying to run black-forest-labs/FLUX.2-dev through Optimum-Intel’s OpenVINO export path, but export fails before conversion completes.

Environment:
optimum-intel 1.27.0
optimum 2.1.0
openvino 2026.2.0
diffusers 0.38.0
transformers 4.57.6

Model:
black-forest-labs/FLUX.2-dev

Config uses:
Flux2Pipeline
Mistral3ForConditionalGeneration
PixtralProcessor
Flux2Transformer2DModel
AutoencoderKLFlux2

Error:
AttributeError: Could not find the attribute named "vocab_size" in the normalized config.

I'm using an Intel Arc Pro B50. The price/performance and images/energy for that GPU is well above all others hence the want.

Start by reproducing the failure on black-forest-labs/FLUX.2-dev with Flux2Pipeline and the listed Optimum-Intel, OpenVINO, Diffusers, and Transformers versions. Trace the OpenVINO export path for the named model components and investigate the normalized-config vocab_size error. Done means the model exports successfully through that path.

Written by the indexing model from the issue text.