Flux2Pipeline loader ignores compiled assets for the text encoder, decoder and optional encoder, and hangs on AOT bundles

### Model name

Flux.2 Klein

### Command run

```shell
Flux2Pipeline(from:) resolves the transformer through ModelBundle.resolveAssetURL, so a compiled .aimodelc is found when the bundle was produced with coreai-build compile. The text encoder and VAE decoder URLs are built with a raw appendingPathComponent(path) from the metadata instead, so on an iOS bundle the loader asks AIModel(contentsOf:) for TextEncoder.aimodel, which does not exist next to TextEncoder.aimodelc. That call never returns and never throws: the app sits at 0% CPU with no log output, which took a while to diagnose on device.

The optional VAE encoder has the same raw path and is not existence-checked, so a text-only export (no img2img components) still gets a non-nil encoder pointing at a missing file, and the first img2img request fails at runtime with a "Missing hash file" error instead of the pipeline reporting that img2img is unavailable.

Repro: export FLUX.2 Klein for iOS, compile the components with coreai-build compile --platform iOS, remove the .aimodel IR directories as a shipping app would, and call Flux2Pipeline(from:) on device. A ready-made bundle is at https://huggingface.co/333i/flux2-klein-coreai-ios (the ios/ folder, compiled for h18p with --preferred-compute gpu, IR directories omitted). Pointing Flux2Pipeline(from:) at that folder on an iPhone 17 Pro reproduces the hang on unpatched main and generates normally with the branch above.

Fix, two commits, on my fork since PR creation is limited to collaborators: https://github.com/apple/coreai-models/compare/main...james-333i:coreai-models:fix-flux-loader-compiled-assets

The text encoder and decoder go through resolveAssetURL, and the encoder is resolved and existence-checked, becoming nil when absent so supportsImageToImage reports the truth. Verified on an iPhone 17 Pro with both a text-only and a full bundle. Happy to open it as a PR if that becomes possible.
```

### macOS / iOS target

iOS 27.0 Beta 8

### Xcode version

Xcode 27 Beta 6

### Python / uv version

uv 0.12.9, python 3.11.2

### Full error output

```shell
Model not found
```

### Anything else?

_No response_

Start at Flux2Pipeline(from:) and trace how ModelBundle.resolveAssetURL differs from the raw appendingPathComponent paths used for the text encoder, VAE decoder, and optional encoder. Review the linked fork comparison as the reported reference, then verify that compiled .aimodelc assets load and that a missing optional encoder becomes nil so supportsImageToImage reports accurately.

Written by the indexing model from the issue text.