feat: add period tracker with calendar, predictions, fertility tracking, and sharing

Full period tracking system for the fitness measure page:
- Period logging with start/end dates, edit/delete support
- EMA-based cycle and period length predictions (α=0.3, 12 future cycles)
- Calendar view with connected range strips, overflow days, today marker
- Fertility window, peak fertility, ovulation, and luteal phase visualization
- Period sharing between users with profile picture avatars
- Cycle/period stats with 95% CI below calendar
- Redesigned profile card as inline header metadata with Venus/Mars icons
- Collapsible weight and period history sections
- Full DE/EN i18n support

src-tauri/tauri.conf.json

@@ -1,7 +1,7 @@
 {
   "productName": "Bocken",
   "identifier": "org.bocken.app",
-  "version": "0.2.1",
+  "version": "0.3.0",
   "build": {
     "devUrl": "http://192.168.1.4:5173",
     "frontendDist": "https://bocken.org"