fix: correct dose ID generation for empty takenBy arrays (#105)

The takenBy field is a string[]. Empty arrays [] are truthy in JavaScript,
causing d.takenBy ? [...] patterns to generate dose IDs with trailing
hyphens (e.g., '5-0-173...-') instead of base IDs ('5-0-173...').

This mismatch between ID generation and computeMissedPastDoseIds (which
correctly uses .length > 0) caused doses to always appear as missed.

Changes:
- Add expandDoseIds() helper function using correct .length > 0 check
- Replace 8 buggy inline patterns in DashboardPage.tsx
- Refactor SchedulePage.tsx to use shared expandDoseIds()
- Add backend startup repair to strip trailing hyphens from existing IDs
- Add 12 new tests (6 frontend + 6 backend)

frontend/src/utils/schedule.ts

@@ -446,6 +446,18 @@ export function isDoseDismissed(doseId: string, dismissedUntilDate: string | und
  * @param dismissedDoses - Set of dose IDs individually dismissed
  * @returns Array of dose IDs that are missed
  */
+/**
+ * Compute the full set of dose IDs for a list of doses, correctly handling
+ * per-intake takenBy arrays. Empty arrays produce base IDs (no suffix),
+ * non-empty arrays produce one ID per person with a `-person` suffix.
+ */
+export function expandDoseIds(doses: ReadonlyArray<{ id: string; takenBy: string[] }>): string[] {
+	return doses.flatMap((d) => {
+		const takenByArray = Array.isArray(d.takenBy) ? d.takenBy : [];
+		return takenByArray.length > 0 ? takenByArray.map((p) => `${d.id}-${p}`) : [d.id];
+	});
+}
+
 export function computeMissedPastDoseIds(
 	pastDays: ReadonlyArray<{
 		meds: ReadonlyArray<{