feat: HDMI refresh boost per display, with a Saved displays screen

Rates are saved per display (EDID ID) and loaded by the hotplug script
for whichever display is connected. The item is on only while the
connected display is boosted; unticking removes just that one. The app
lists the saved displays and removes any of them (hdmi-forget).

CHANGELOG.md

@@ -7,13 +7,17 @@ one per merged pull request.
 
 ## 2.1.0 - 2026-09-26
 
-- **feat: HDMI refresh boost only for the display it was set up for**
+- **feat: HDMI refresh boost per display, with a Saved displays screen**
   - The EDID override was on the kernel command line, so any display on that
-    HDMI port got the first display's timings. It's now loaded at boot and
-    at every hotplug only when the connected display is the one it was
-    tested on (its ID read over DDC); another display, or unplugging, puts
-    the port back on the display's own EDID. No initramfs or boot loader
-    change any more. An existing setup is moved over when re-applied (`a`).
+    HDMI port got the first display's timings. Rates are now saved per
+    display and loaded at boot and at every hotplug for the display that's
+    connected (its ID read over DDC); a display without saved rates, or
+    unplugging, puts the port back on the display's own EDID. No initramfs
+    or boot loader change any more. An existing setup is moved over when
+    re-applied (`a`).
+  - The item shows on only while the connected display is boosted, so a new
+    display can be set up by ticking it; unticking removes only that one.
+  - The app lists the saved displays (▶ on the item) and removes any of them.
 
 ## 2.0.3 - 2026-09-26