fix(medications): size weekly-cadence supply runway correctly

`estimateDailyDoseCount` only special-cased FREQ=MONTHLY and FREQ=YEARLY.
A modern FREQ=WEEKLY rrule (the encoding the create path stores, with an
empty daysOfWeek) fell through to the legacy branch at seven days per week,
so a once-weekly injection counted as one dose per day. The detail card's
"lasts about N days" and the daily low-stock job — which share this math —
fired reorder alerts roughly seven times too early (fourteen for bi-weekly).

Parse FREQ=WEEKLY honouring INTERVAL and BYDAY count:
perDay += (times * bydayCount) / (7 * interval).

src/components/medications/__tests__/supply-runway.test.ts

@@ -68,6 +68,43 @@ describe("estimateDailyDoseCount", () => {
     ).toBeCloseTo(1 / 30);
   });
 
+  it("treats a once-weekly RRULE as one dose per 7 days", () => {
+    // FREQ=WEEKLY;BYDAY=MO is the modern once-weekly injection encoding;
+    // it must NOT fall through to the daysPerWeek=7 legacy branch.
+    expect(
+      estimateDailyDoseCount([
+        schedule({ timesOfDay: ["08:00"], rrule: "FREQ=WEEKLY;BYDAY=MO" }),
+      ]),
+    ).toBeCloseTo(1 / 7);
+  });
+
+  it("halves a bi-weekly RRULE via INTERVAL=2 (one dose per 14 days)", () => {
+    expect(
+      estimateDailyDoseCount([
+        schedule({
+          timesOfDay: ["08:00"],
+          rrule: "FREQ=WEEKLY;INTERVAL=2;BYDAY=MO",
+        }),
+      ]),
+    ).toBeCloseTo(1 / 14);
+  });
+
+  it("counts each BYDAY pick on a weekly RRULE (Mon+Thu → 2 per 7 days)", () => {
+    expect(
+      estimateDailyDoseCount([
+        schedule({ timesOfDay: ["08:00"], rrule: "FREQ=WEEKLY;BYDAY=MO,TH" }),
+      ]),
+    ).toBeCloseTo(2 / 7);
+  });
+
+  it("defaults a weekly RRULE with no BYDAY to one pick per week", () => {
+    expect(
+      estimateDailyDoseCount([
+        schedule({ timesOfDay: ["08:00"], rrule: "FREQ=WEEKLY" }),
+      ]),
+    ).toBeCloseTo(1 / 7);
+  });
+
   it("sums across multiple schedules", () => {
     expect(
       estimateDailyDoseCount([

src/components/medications/detail/supply-runway.ts

@@ -46,6 +46,25 @@ export function estimateDailyDoseCount(schedules: RunwaySchedule[]): number {
       perDay += times / 365;
       continue;
     }
+    // FREQ=WEEKLY;BYDAY=…;INTERVAL=… is the modern weekly encoding (the
+    // create path stores the cadence on the rrule and leaves daysOfWeek
+    // empty). Honour the BYDAY pick count and the week INTERVAL: a
+    // once-weekly injection is one dose per 7 days, a bi-weekly one per
+    // 14. Without this branch a weekly rrule fell through to the legacy
+    // daysOfWeek fallback below with daysPerWeek=7, over-estimating the
+    // rate ~7× (≈14× bi-weekly) and firing low-stock alerts far too early.
+    if (/FREQ=WEEKLY/.test(rrule)) {
+      const byday = /BYDAY=([^;]+)/.exec(rrule);
+      const bydayCount =
+        byday && byday[1].length > 0 ? byday[1].split(",").length : 1;
+      const intervalMatch = /INTERVAL=(\d+)/.exec(rrule);
+      const interval =
+        intervalMatch && Number(intervalMatch[1]) >= 1
+          ? Number(intervalMatch[1])
+          : 1;
+      perDay += (times * bydayCount) / (7 * interval);
+      continue;
+    }
     const { daysOfWeek, intervalWeeks } = parseScheduleRecurrence(s.daysOfWeek);
     const daysPerWeek = daysOfWeek.length > 0 ? daysOfWeek.length : 7;
     const weeks = intervalWeeks >= 1 ? intervalWeeks : 1;