feat(rates): multi-tier distance band entry in last-mile rate form

- tierList field type in rule-engine form dialog (add/remove rows,
  overlap + open-ended validation, From km auto-continues)
- create submits one rate row per tier sequentially
- editing a band row keeps the single From/To/value form

apps/edr-freight-web/backoffice/src/pages/ruleEngine/config/resources.ts

@@ -17,7 +17,7 @@ export type ColumnFormat =
   | "entityLabel"
   | "rateLabel";
 
-export type FormFieldType = "text" | "number" | "boolean" | "date" | "email" | "select" | "multiselect" | "textarea" | "radio";
+export type FormFieldType = "text" | "number" | "boolean" | "date" | "email" | "select" | "multiselect" | "textarea" | "radio" | "tierList";
 
 export interface ResourceColumn {
   id: string;
@@ -1022,6 +1022,19 @@ export const RULE_ENGINE_RESOURCES: RuleEngineResourceConfig[] = [
         showWhen: { field: "appliesTo", equals: ["LAST_MILE"] },
         getInitialValue: (record) => String(record.currency ?? "ETB"),
       },
+      // ── Distance tiers (create only — the page swaps this for the single
+      // From/To/value fields when editing an existing band row). Each tier
+      // becomes its own rate row, so every band keeps edit/delete/approval. ──
+      {
+        name: "tiers",
+        label: "Distance tiers",
+        type: "tierList",
+        required: true,
+        description:
+          "One rate per distance range. To km is exclusive (0–30 then 30+); leave the last tier's To km empty for no upper limit.",
+        showIf: (v) =>
+          v.appliesTo === "LAST_MILE" && v.lastMileMode === "CONTAINER",
+      },
       // ── Container type — Container freight, container-kind intercity, and
       // the empty-container return surcharge (20ft vs 40ft price differently) ─
       {