feat: Add Clear Missed Doses feature (#28)

- Add dismissed column to dose_tracking table schema
- Add POST /doses/dismiss endpoint for batch dismissing
- Add DELETE /doses/dismiss endpoint to un-dismiss all
- Add frontend dismissedDoses state and missedPastDoseIds useMemo
- Add Clear missed button with confirmation dialog
- Add CSS styles for .past-days-header and .clear-missed-btn
- Add i18n translations for en/de
- Add 5 tests for dismiss endpoints
- Update test schemas with dismissed column

Allows users to acknowledge missed doses without deducting stock.
Closes #28

backend/src/db/schema.ts

@@ -115,4 +115,5 @@ export const doseTracking = sqliteTable("dose_tracking", {
   doseId: text("dose_id", { length: 255 }).notNull(), // e.g. "med-5-1-86400000-1735200000000"
   takenAt: integer("taken_at", { mode: "timestamp" }).notNull().default(sql`(strftime('%s','now'))`),
   markedBy: text("marked_by", { length: 100 }), // null = user, "Daniel" = via share link
+  dismissed: integer("dismissed", { mode: "boolean" }).notNull().default(false), // true = missed dose acknowledged without taking
 });