feat: HDMI refresh boost (Steam Machine, pinned kernel)

The pinned 7.1.6 kernel doesn't read the extra EDID block (HDMI Forum
EEODB) where monitors list their fast modes, and does no HDMI 2.1, so HDMI
displays often stay at 60 Hz. The new menu item reads the display's EDID
over DDC, calculates the highest rate that fits HDMI 2.0 at the desktop
resolution (rounded down to ten, plus the hundred below as a safe option),
tests each step live with a confirmation, and makes the confirmed ones
permanent through drm.edid_firmware (Limine, sdboot-manage or GRUB).

TECHNICAL.md

@@ -229,6 +229,48 @@ into the kernel directory yourself.
 Unticking it removes the pin and runs `sudo pacman -Syu`, which brings the
 kernel back to CachyOS's current version; the files stay for next time.
 
+## HDMI refresh boost (Steam Machine)
+
+With the pinned kernel (7.1.6), HDMI displays often stay at 60 Hz. Two
+reasons:
+
+- Monitors list their fast modes in an extra EDID block, announced by the
+  HDMI Forum EEODB data block. 7.1.6 only reads the first extension block,
+  so it never sees them. Newer kernels do.
+- Their fastest modes need HDMI 2.1 (FRL). 7.1.6's amdgpu only does HDMI
+  2.0 (TMDS, at most 600 MHz), but a mode with the display's own shortest
+  blanking at a slightly lower rate often fits.
+
+The menu item (only on a Steam Machine with the pinned kernel, never
+ticked by default, run from the desktop in Konsole):
+
+1. Takes the desktop resolution from KDE (`kscreen-doctor -j`) and reads the
+   display's complete EDID over DDC (`i2ctransfer`, segment pointer 0x30).
+   A live EDID left by an earlier test is cleared first.
+2. Calculates the highest rate that fits: the display's TMDS limit (HDMI
+   Forum VSDB, capped at amdgpu's 600 MHz), its shortest blanking at that
+   resolution and its maximum refresh (range limits, VRR maximum). Steps:
+   that rate rounded down to ten, and the hundred below it as a safe option.
+   Rates the display already lists, or that aren't faster than what works
+   now, are left out.
+3. Builds the EDID: all of the display's blocks, the block count and EEODB
+   fixed, plus a DisplayID block with the steps.
+4. Loads it live (debugfs `edid_override`, `trigger_hotplug`) and switches
+   to each step, lowest first. Each one needs a "y" within 15 s
+   (`WIZARD_HDMI_CONFIRM_SECONDS` for tests); anything else switches back
+   and stops.
+5. Makes it permanent with only the confirmed steps:
+   `/usr/lib/firmware/edid/steamify-<connector>.bin`, in the initramfs via
+   `/etc/mkinitcpio.conf.d/90-steamify-edid.conf` (amdgpu loads from there),
+   and `drm.edid_firmware=<connector>:edid/steamify-<connector>.bin` on the
+   kernel command line: `/etc/default/limine` (`limine-mkinitcpio`),
+   `/etc/sdboot-manage.conf` or `/etc/default/grub`.
+
+The display's manufacturer, model and serial are stored; re-applying with
+another display connected tests that one instead. Turning it off removes
+the files and the parameter and rebuilds. Untick it before removing the
+kernel pin: newer kernels read the EDID themselves and can do HDMI 2.1.
+
 ## BIOS updates (Steam Machine)
 
 The **Update BIOS** item is only shown on a Steam Machine and is never ticked
@@ -298,6 +340,7 @@ immediately, which can turn into a loop - see
 | `lib/bios.sh` | Update BIOS (Steam Machine, opt-in): current/newest version, double confirmation, fwupd |
 | `lib/cec.sh` | HDMI-CEC: Valve's `cecd` and friends from its `holo` repository |
 | `lib/steam-machine.sh` | Steam Machine support: LED driver, LED access, steamos-manager; kernel pin |
+| `lib/hdmi-refresh.sh` | HDMI refresh boost (Steam Machine, pinned kernel): EDID over DDC, calculated steps, live test, `drm.edid_firmware` |
 | `.github/tools/bundle.sh` | Builds the single-file version (`dist/steamify.sh`) |
 | `.github/workflows/bundle.yml` | Builds and checks it on every push; publishes it on `main` |