#23 — Rules attachment UI (shared across all entity forms)

[bobinush]

Every entity form — Polygons, Roads and POIs — must include a Rules section
where the admin can attach one or more rules to that entity.

Acceptance criteria:

• A dropdown lists all available rules (name + severity)
• Selecting a proximity rule reveals a "Distance (metres)" number field — this value is per-attachment (the same rule can be attached to different entities with different distances)
• Clicking "Add" appends a chip showing the rule name, severity badge and distance (if set); duplicate attachments are rejected with a warning
• Each chip has a remove button
• The rules array (e.g. [{ ruleId, distanceMeters }]) is included in every POST and PUT entity payload
• When editing an existing entity its saved rules are pre-populated
• If no rules have been defined yet the section shows a note directing the admin to the Rules tab