Rework form generation around incidents and templates instead of extractions

[chetanr25]

Rework form generation around incidents and templates instead of extractions

Background

Form generation still pointed at extract_id and a closed form_type enum, both left over from before templates were user-registered and before extraction fed into a stored incident. It also had two separate endpoints for generating one form versus all forms, which no longer makes sense once generation is just a lookup against the incident's contract document.

What needs to change

• Merge generate/all and generate/{form_type} into one POST /forms/generate that takes an incident_id and a list of template_ids. Omitting template_ids generates everything the readiness matrix reports as ready.
• Point generation at incident_id instead of extract_id, since the contract document now lives on the incident row, not the extraction.
• Since generation is pure lookup and draw (schema fields read the contract path, static fields stamp saved text, manual and open fields read custom_fields), no LLM runs here at all, so a whole batch should complete in seconds even for many templates.
• Templates that are not ready get skipped with a reason instead of failing the whole batch, unless force_partial is set.
• Unify the response shapes so a single form and a batch form both return the same FormRecord, with template_id, form_type, and batch_id all present.
• Add GET /forms/batch/{batch_id}/download so a batch of generated forms can be pulled as one archive instead of fetching each form's PDF individually.