feat: Add tea powder amount (teaspoons) to tracking

- Add new field 'Menge Tee-Pulver (Teelöffel)' to track form
- Add teaspoons property to entry data model
- Update addEntry() to include teaspoons (default: 1)
- Update handleTrackFormSubmit() to read teaspoons from form
- Display teaspoons in recent entries (e.g., '2 Tassen (1.5 TL)')
- Add migration for existing entries without teaspoons field
- Input allows decimal values (step=0.5) for half teaspoons

Co-authored-by: trevor1969 <trevor1969@users.noreply.github.com>

index.html

@@ -101,6 +101,11 @@
                         <input type="number" id="track-amount" min="1" max="10" value="1" required>
                     </div>
                     
+                    <div class="form-group">
+                        <label for="track-teaspoons">Menge Tee-Pulver (Teelöffel)</label>
+                        <input type="number" id="track-teaspoons" min="0" max="10" value="1" step="0.5">
+                    </div>
+                    
                     <div class="form-group">
                         <label for="track-notes">Notizen</label>
                         <textarea id="track-notes" rows="3" placeholder="z.B. Mit Honig, besonders stark..."></textarea>