feat(srs): switch ladder to +3/+7 and enforce rest‑day logic

apps/api/src/catalog.ts

@@ -10,7 +10,7 @@
  * so relabelling a problem is enough to move it and titles stay readable.
  * The `problem` label is what marks a sub-issue as curriculum.
  */
-import { addDays } from "./srs.ts";
+import { workingDay } from "./srs.ts";
 import type { GitHub } from "./github.ts";
 
 const TITLE_RE = /^LC (\d+) · (.+)$/;
@@ -18,7 +18,7 @@ const TITLE_RE = /^LC (\d+) · (.+)$/;
 const DIFFICULTIES = ["easy", "medium", "hard"] as const;
 const SETS = ["core", "optional", "deferred"] as const;
 
-/** Deferred Hards enter the queue from this date, two per day. */
+/** Deferred Hards enter the queue from this date, two per working day. */
 const DEFER_FROM = "2026-09-28";
 
 export interface ReconcileReport {
@@ -96,9 +96,10 @@ export async function reconcileCatalog(db: D1Database, gh: GitHub): Promise<Reco
         continue;
       }
       const lc = Number(m[1]);
-      // Two deferred Hards per day from DEFER_FROM, in catalog walk order —
-      // applied only when the row is first created (SRS owns it afterwards).
-      const defer = set === "deferred" ? addDays(DEFER_FROM, Math.floor(deferredSeen / 2)) : null;
+      // Two deferred Hards per WORKING day from DEFER_FROM, in catalog walk
+      // order — applied only when the row is first created (SRS owns it
+      // afterwards). Sunday is skipped like every other scheduled date.
+      const defer = set === "deferred" ? workingDay(DEFER_FROM, Math.floor(deferredSeen / 2)) : null;
       if (set === "deferred") deferredSeen++;
       statements.push(
         db