Frosted glass shell, driven by gsettings

[wayne-tbl]

The frosted-glass look for the shell, built from gsettings keys rather than compiled into a stylesheet, and the client side of phoc's background blur.

Updated at review request: phosh's own stylesheets are no longer touched. common.css, adwaita-dark.css and adwaita-hc-light.css are byte-identical to forky on this branch. The glass is a set of whole stylesheets of its own — common-furios.css, adwaita-dark-furios.css, adwaita-hc-light-furios.css, adwaita-light-furios.css — loaded in their place only when the user asks for the theme.

The switch

glass-theme is a new boolean, off by default. With it off, phosh is left exactly as it is: phosh_style_manager_get_stylesheet() picks the sheet the way it does today, the generated CSS contains only the two accent colours phosh generates itself, gtk-application-prefer-dark-theme is not touched, no surface asks the compositor for blur, and the generated ~/.config/gtk-4.0/gtk.css is removed so applications do not keep a look that is no longer in use. Turning it on and off again returns the shell to stock without a restart.

The one FuriOS behaviour that stays live either way is the free-form accent colour: it widens phosh's own accent setting rather than being part of the glass.

• protocol: add the blur request to layer-shell-effects — version 4 of zphoc_layer_shell_effects_v1, in sync with phoc.
• phosh-wayland: bind layer-shell-effects version 4
• layersurface: ask the compositor to blur the background — mirrors the alpha surface. The FuriOS global is bound only if the compositor offers it, and is deliberately left out of the "lacks needed globals" fatal check, so the shell still starts against a stock phoc and simply gets no blur.
• util: add the glass gsettings keys / data: add the glass gsettings keys — the io.furios.phosh.shell keys: the glass-theme switch itself, blur radius, glass opacity, lightness and accent wash, text and shadow colours, and a free-form accent that overrides the nine swatches. The look is retuned with gsettings rather than by rebuilding a stylesheet.
• stylesheet: add a frosted glass variant — translucent surfaces, soft shadows and inset hairline highlights on the drawer, notifications, media player and OSD, radii normalised. The panel is a single glass sheet: stacking translucent layers on each other is what made the drawer read as solid.
• stylesheet: add a light glass variant — phosh has no light stylesheet of its own, so this one has no upstream counterpart to leave alone.
• stylesheet: keep high contrast solid — glass is the opposite of what the high contrast variant is for, so its -furios copy puts the translucent surfaces back to opaque.
• style-manager: build the shell's glass from the gsettings keys — loads the -furios sheets when the theme is on and follows org.gnome.desktop.interface color-scheme while it is, so the dark mode quick setting swaps the look live. Text is pure black on light and pure white on dark, because what sits behind it is a wallpaper the theme knows nothing about; the shadow takes the opposite of the text colour actually in use rather than of the scheme.
• style-manager: generate a GTK4 stylesheet from the same keys
• top-panel: ask for background blur — only while the theme is on: behind an opaque panel the blur would not show and the compositor would still pay for it.
• lockscreen: frost the keypad page — only once the user has swiped up. The info page is a wallpaper with a clock on it and the lock screen sits above its own background surface, not above the running apps, so blurring it only makes the picture worse.

Two things worth a reviewer's eye. The -furios sheets are whole stylesheets rather than overlays on phosh's: it costs some duplication in common-furios.css, and buys a guarantee that with the theme off nothing of ours is in the cascade at all. And generating ~/.config/gtk-4.0/gtk.css is deliberately its own commit: it makes the theme phone-wide rather than shell-only, which is a decision worth taking separately from the shell theme. It refuses to touch a file it did not write, and applications pick changes up when they next start, since GTK4 reads the user stylesheet once and does not watch it.

Pairs with FuriLabs/phoc glass-theme, which implements the blur. Because of the version guard the two can land in either order — against a stock phoc the panels are translucent and simply not frosted.
Switched on from FuriLabs/gnome-control-center#6, which carries the toggle.

12 commits, off forky. Tested on an FLX1 across many boots, including rotation, dark/light switching and the accent swatches.

[wayne-tbl]

The thirteen feature branches build merged. Three conflicts, all the same shape: two branches appending a key at the same spot in a gschema, and the paired signal handlers in phoc desktop.c. Each resolved by keeping both sides, no code change needed. Merged build runs phoc 17/17 and phosh 42/69, no new failure.

Installed and booted on an FLX1 and an FLX1s. With glass-theme off the shell is indistinguishable from a build without it. Blur cost is on FuriLabs/phoc#3.