fix(badge): zero-init DIB bits buffer to eliminate black square

CreateDIBSection does not guarantee zeroed memory. Uninitialized bytes
with non-zero RGB but zero alpha were getting alpha=255 set by the
existing pixel loop, causing a black square around the badge circle.
Zeroing with write_bytes before GDI drawing ensures only explicitly
painted pixels are opaque.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src-tauri/src/lib.rs

@@ -182,6 +182,11 @@ fn set_badge_count(count: u32, window: tauri::Window) -> Result<(), String> {
                 let hbm_color =
                     CreateDIBSection(Some(hdc), &bmi, DIB_RGB_COLORS, &mut bits, None, 0)
                         .map_err(|e| e.to_string())?;
+                // Zero-init so undrawn pixels are fully transparent (CreateDIBSection
+                // does not guarantee zeroed memory; garbage bytes cause a black square).
+                if !bits.is_null() {
+                    std::ptr::write_bytes(bits as *mut u8, 0, (size * size * 4) as usize);
+                }
                 let old_bm = SelectObject(hdc, hbm_color.into());
 
                 let hbrush = CreateSolidBrush(COLORREF(0x003030DD));