ADR template

Copy this into docs/adr/NNNN-short-title.md and into splick-backend/docs/adr/ if the decision changes the backend runtime. Number is the next integer. Status starts as Proposed.

# ADR NNNN: Title

## Status

Proposed | Accepted | Superseded by ADR-XXXX

## Context

What forced a decision. Constraints, not a design dump.

## Decision

The choice, in a few numbered points.

## Consequences

Positive, negative, and the rollback that does not destroy committed data.