Set keyboard brightness to fixed values of 0, 1, 25 and 100.

[sockbot]

Fixes #5414

This PR sets keyboard backlight keys to use the fixed values of 0, 1, 25, and 100 percent corresponding to off, low, medium, and high.

Limiting the backlight settings to off, low, medium and high on my hardware provides a simplified and practical user experience to get an appropriate backlight level in fewer presses compared to steps of 10%. In addition, since the backlight strength is not linear, more discrete options do not add functionality (values of 50-100 are almost identical).
I chose the values of 0, 1, 25 and 100 because these subjectively looked like equidistant levels of brightness across the range.

Because this PR only exposes keyboard backlight values of off, low, medium and high I replaced the 100% scale bar with a simple text display:

Testing

• Use keyboard brightness up and down keys to cycle brightness through OFF, LOW, MEDIUM, and HIGH.

Tested on MacBook Air 2014. Testing on additional hardware is welcome (and desired).

┌──────────────────────Hardware──────────────────────┐
 PC: MacBook Air (11-inch, Mid 2013/Early 2014) (1.0)
│ ├: Intel(R) Core(TM) i5-4260U (4) @ 2.70 GHz
│ ├: Intel Haswell-ULT Integrated Graphics Controller @ 1.00 GHz [Integrated]
│ ├󱄄: 1366x768 in 12", 60 Hz [Built-in]
│ ├󰋊: 82.80 GiB / 231.74 GiB (36%) - btrfs
│ ├: 1.81 GiB / 3.76 GiB (48%)
└ └󰓡 : 424.20 MiB / 1.88 GiB (22%)
└────────────────────────────────────────────────────┘

┌──────────────────────Software──────────────────────┐
 OS: Omarchy 3.6.0
│ ├󰘬: master
│ ├󰔫: stable
│ ├: Linux 6.19.12-arch1-1
│ ├: Hyprland 0.54.3 (Wayland)
│ ├: ghostty 1.3.1-arch2
│ ├󰏖: 1188 (pacman)
│ ├󰸌: Kanagawa ●●●●●●●●
└ └: JetBrainsMono Nerd Font (9pt)
└────────────────────────────────────────────────────┘

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[kuro-toji]

Thanks for the feedback! To clarify, this PR (#5424) is specifically the PR that addresses the keyboard backlight issue using the fixed values of 0, 1, 25, and 100 percent.

You mentioned that you've already created a PR that specifically addresses the keyboard backlight issue. Could you point me to that PR? If it's a separate PR that supersedes this one, I can close this PR and let the discussion happen there instead.

Regarding your other feedback about setting minimum brightness to 1 instead of 0 — I agree that including 1 as a minimum level is important for cases where users want some backlight but not full off. The current values (0, 1, 25, 100) do include 1 as the lowest "on" level. Would you like me to adjust the brightness levels further?

Let me know if you'd prefer this PR to focus on a different change, or if I should keep the keyboard backlight changes here.