Refresh user stories and AI-autonomous development guidance

## Outcome

User stories and implementation guidance provide enough context, constraints, and verification detail for engineers and autonomous coding agents.

## Scope

- Rewrite stories around user outcomes and measurable acceptance criteria
- Document architecture boundaries, conventions, and decision records
- Define required tests, observability, rollout, and documentation expectations
- Provide feature templates and representative implementation examples

## Acceptance criteria

- [ ] Scope is decomposed into independently deliverable child issues.
- [ ] Architecture and API decisions are linked from this issue.
- [ ] Test, documentation, observability, rollout, and failure behavior are defined where applicable.
- [ ] Epic exit criteria are verified before closure.

## Planning note

This is a 2026 GovTool revamp work item. Its child features and tasks should be added as the scope is refined.

Start by decomposing this 2026 GovTool revamp epic into independently deliverable child issues. Define and link the relevant architecture and API decisions, then specify applicable tests, documentation, observability, rollout, and failure behavior. Done means the child scope and exit criteria are verified before closure; no files or tests are named yet.

Written by the indexing model from the issue text.