fix(overlay): enforce text wrap width to prevent overflow beyond screen

Add `gtk_label_set_width_chars` to set a concrete width for label allocation,
ensuring long sentences wrap within the configured max-chars bubble width
instead of extending off-screen.

README.md

@@ -64,7 +64,7 @@ Use `--output=both` to keep terminal output as well:
 ./scripts/distrobox/run.sh --mode=vad --output=both
 ```
 
-In VAD mode, a 500 ms pause finalizes the current caption and starts the next line. The overlay keeps up to six completed lines above the active provisional caption; each completed line remains visible for at least three seconds and gradually fades from white to a restrained gray as it ages. If a seventh line arrives sooner, the hard six-line cap removes the oldest. Text is left-aligned inside the centered, fixed-width dark bubble. Pointer input passes through the window by default. Empty completed captions hide the overlay.
+In VAD mode, a 500 ms pause finalizes the current caption and starts the next line. The overlay keeps up to six completed lines above the active provisional caption; each completed line remains visible for at least three seconds and gradually fades from white to a restrained gray as it ages. If a seventh line arrives sooner, the hard six-line cap removes the oldest. Text is left-aligned inside the centered, fixed-width dark bubble and wraps at its configured width instead of extending off-screen. Pointer input passes through the window by default. Empty completed captions hide the overlay.
 
 To build outside the helper script, install GTK4 and GTK4 Layer Shell development packages, then run: