Allow users to choose the AI model when filling forms

[jansans04]

Allow users to choose the AI model when filling forms

Backend for the model picker in #502. The frontend needs to know which models exist, pick one per request, and install one that is missing.

Why

• Fill only ever used the model set in OLLAMA_MODEL. Changing it meant editing .env and restarting.
• A model that was not installed came back as a generic 500 from the filler.
• There was no way to download a model through the API, so a first-time user had to shell into the Ollama container.

What changed

• GET /api/v1/forms/models returns current_model and a list of {name, installed, recommended}. Recommended models are always listed, plus anything Ollama has installed. If Ollama is down or answers with something unreadable, it still returns the recommended models, all with installed: false.
• POST /api/v1/forms/fill takes an optional model. Without it, OLLAMA_MODEL is used as before.
• A model that is not installed returns 422 MODEL_NOT_INSTALLED instead of a 500. Async fill jobs keep the same code instead of TASK_FAILED.
• POST /api/v1/forms/pull takes a model name and streams Ollama's progress as NDJSON. It ends with {"status":"success"}. If the pull fails after the stream has started, the error is sent as an error line and no success line follows, since the HTTP status is already committed.
• Model names are validated on fill and pull: trimmed, not empty, at most 128 characters, and limited to the characters Ollama model names use.
• OLLAMA_PULL_TIMEOUT is separate from OLLAMA_TIMEOUT, because a download takes far longer than an inference call. Both are in docker/.env.example.
• Contracts and docs/AI_MODELS.md updated.

Notes

• GET /forms/models changed shape: models used to be list[str] and is now a list of objects. Inside this repo only the frontend reads it, and fetchModels() already adapts it. Anything outside the repo reading the old shape would break.
• installed and /forms/pull only make sense for Ollama. They are kept in list_models() and pull_model() in forms.py so [FEAT] Support LLM providers other than Ollama on development #716 can move them behind its provider layer, where non-Ollama providers will need a different answer.
• The dropdown is not in this PR. The frontend still needs adjusting to the final response and will follow separately.

Testing

• python -m pytest: 184 passed. New tests cover a pull error mid-stream, invalid model names on fill and pull, MODEL_NOT_INSTALLED in an async job, a malformed tags response, fill without model, and the pull timeout.
• Checked by hand against a running Ollama: .

Part of #502

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[marcvergees]

get rid of this one

[marcvergees]

10 mins? what happens if takes more than 10? how much should it be taking?

[jansans04]

It wasn't a total limit: it's the requests timeout on a streamed response,
so it's the max wait between two chunks, and Ollama sends progress
continuously. But 10 minutes of silence was too generous for a stuck download.

Changes:

• connecting is now limited to 10 s, separate from the idle timeout
• default lowered from 600 to 120 s
• docs and .env.example now describe it as an idle timeout
• added a test for a mid-stream timeout (error line, no success)

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[marcvergees]

It looks 99% good to me. You just gotta change 1 thing and we'll be able to merge it.

Thanks @jansans04 !

[marcvergees]

move this into config.py, general stuff should be allocated together

[marcvergees]

I've already patched it @jansans04.