Ship full-resolution WebP screenshots, drop em dashes everywhere

The screenshots were downscaled to 430 px wide, which made the UI text
blurry. Restore them at native 1292 px as lossless WebP, which is also
half the size of the original PNGs (72 KB against 155 KB for the largest).

Rewrite every em dash in prose, comments, docstrings and interface strings
as ordinary punctuation.

install.sh

@@ -38,7 +38,7 @@ if command -v ydotool >/dev/null; then
      || systemctl --user is-active --quiet ydotoold 2>/dev/null; then
     ok "ydotoold is running (auto-paste ready)"
   else
-    warn "ydotoold is not running — auto-paste will not work"
+    warn "ydotoold is not running, auto-paste will not work"
     say  "systemctl --user enable --now ydotool"
   fi
 fi
@@ -50,7 +50,7 @@ chmod +x "$DIR/dikte.py"
 ok "Command installed: $BIN_DIR/dikte"
 case ":$PATH:" in
   *":$BIN_DIR:"*) ;;
-  *) warn "$BIN_DIR is not on your PATH — for fish: fish_add_path $BIN_DIR" ;;
+  *) warn "$BIN_DIR is not on your PATH. For fish: fish_add_path $BIN_DIR" ;;
 esac
 
 cat > "$APP_DIR/dikte.desktop" <<EOF
@@ -96,7 +96,7 @@ if command -v kwriteconfig6 >/dev/null; then
   say  "next login. Until then open Settings → Shortcut and turn on the"
   say  "built-in listener to use it right away."
 else
-  warn "kwriteconfig6 not found — add the shortcut via System Settings → Shortcuts"
+  warn "kwriteconfig6 not found. Add the shortcut via System Settings > Shortcuts"
 fi
 
 echo