fix: eraser size menu, pointed shape corners, flat tiles for slides (Issues #38, #40, #41, #28)

- #38: the eraser size button opens a menu like the pens: four presets and a slider
  (2–30 mm diameter)
- #41: shape corners stay pointed down to about 14° (miter limit 8 instead of 2)
- #40: page picker tiles are as high as the tallest page needs, so slides get flat tiles;
  the frame follows the page instead of the whole tile
- #28: the fling diagnosis also logs finger starts, mouse buttons and wheel/touchpad events

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/i18n/en.rs

@@ -120,6 +120,7 @@ pub const EN: &[(&str, &str)] = &[
     ("Gitea Release-JSON konnte nicht verarbeitet werden: {e}", "Could not process the Gitea release JSON: {e}"),
     ("Gitea Server-URL:", "Gitea server URL:"),
     ("Gitea-Server antwortete mit HTTP {code}: {body}", "Gitea server responded with HTTP {code}: {body}"),
+    ("GRÖSSE", "SIZE"),
     ("Graphit-Grau", "Graphite gray"),
     ("Größere Schrift (jetzt {size} pt)", "Larger font (now {size} pt)"),
     ("Grün", "Green"),
@@ -256,9 +257,10 @@ pub const EN: &[(&str, &str)] = &[
     ("Quell-PDF ist verschlüsselt", "Source PDF is encrypted"),
     ("Radieren", "Erase"),
     ("Radierer (E oder rechte Maustaste) – darunter: ganze Striche, Teilstrich, nur Textmarker und die Größe", "Eraser (E or right mouse button) – below: whole strokes, partial stroke, highlighter only and the size"),
+    ("Radierer", "Eraser"),
     ("Radierer (Eraser)", "Eraser"),
-    ("Radiergröße {size} mm", "Eraser size {size} mm"),
-    ("Radiergröße {size} mm – tippen für die nächste Größe", "Eraser size {size} mm – tap for the next size"),
+    ("Radiergröße {size} mm – tippen zum Ändern", "Eraser size {size} mm – tap to change"),
+    ("Radiergröße {size} setzen", "Set eraser size to {size}"),
     ("Raute (Rhombus)", "Rhombus"),
     ("Rechteck", "Rectangle"),
     ("Rechts", "Right"),
@@ -314,6 +316,7 @@ pub const EN: &[(&str, &str)] = &[
     ("Stift {number} ({width} mm)", "Pen {number} ({width} mm)"),
     ("Stift {number}", "Pen {number}"),
     ("Stift", "Pen"),
+    ("STUFENLOSE GRÖSSE", "STEPLESS SIZE"),
     ("STUFENLOSE STÄRKE", "STEPLESS WIDTH"),
     ("Stärke auf {width} setzen", "Set width to {width}"),
     ("System", "System"),