luci-theme-material: refining hide/show buttons

[owlsy]

Changes

• Change mouse icon on hide/show button from a text cursor to a pointer.
• Fix the hide/show buttons not being the same min-width due to text being different sizes.
• Create larger hide/show buttons for smaller screens, for the same behaviour as luci-theme-bootstrap.
• Slightly fade "show" button: no variable for disabled opacity like luci-theme-bootstrap, assuming 0.7.
• Remove that fade when hovering over the button.

Notes

• Tested on: Safari Version 26.4 (21624.1.16.11.4), OpenWrt 25.12.2 r32802-f505120278 / LuCI openwrt-25.12 branch 26.087.74782~b3f192d
• Could not find PKG_VERSION in the Makefile.
• Large number of code authors, unsure who to select for feedback.
• Part of a collection of pull requests based on luci-theme: Refined CSS for all themes, including adding larger hide/show buttons for smaller screens to all themes #8491

Checklist

• This PR is not from my main or master branch 💩, but a separate branch ✅
• Each commit has a valid ✒️ Signed-off-by: <my@email.address> row (via git commit --signoff)
• Each commit and PR title has a valid 📝 <package name>: title first line subject for packages
• Incremented 🆙 any PKG_VERSION in the Makefile
• Tested on: (architecture, openwrt version, browser) ✅
• ( Preferred ) Mention: @ the original code author for feedback
• ( Preferred ) Screenshot or mp4 of changes:
• Description: (describe the changes proposed in this PR)

[owlsy]

Should I wait for #8508 before rebasing on master and updating this pull request?

Edit: Just going to make a new pull request as I can't remove the latest merge commit, I had trouble figuring it out without making more of a mess.

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[owlsy]

Messed up the commits and couldn't resolve it. Closing and trying again with #8519.