Screenshot and screen recorder shell support

[wayne-tbl]

The shell side of the two capture quick settings. Updated again at review request (18 Aug): the exported symbols are gone — the plugin now reaches the shell over D-Bus instead. The quick settings themselves live in FuriLabs/furios-phosh-plugins#2.

src/phosh-exported-symbols.txt.in is byte-identical to forky again, so nothing here can be caught out by an upstream ABI change.

• shell: add a helper to fold the top panel — the shell already folds the drawer on lock, from inside phosh_shell_set_locked(); this lifts it into a function so the screenshot manager can do the same. Not exported; called from within the shell only.
• screenshot-manager: open the shot from its notification — click to open in the default image viewer, with a thumbnail of what was captured.
• screenshot-manager: add a delayed screenshot — otherwise a shot taken from the quick settings is a picture of the quick settings. The countdown runs in a silent transient notification, closed 350 ms before the shutter: the banner is a layer surface like any other and a shot taken sooner catches it on its way out.
• screenshot-manager: add a FuriOS interface for the delayed screenshot — new. io.furios.Shell.Screenshot.ScreenshotDelayed(u delay), which folds the drawer and starts the countdown, returning as soon as the countdown starts.
• shell: add the screen capture gsettings — the screenshot delay, and the recorder's framerate, speed, codec, bitrate, audio source and touch drawing.

Why a new interface rather than a method on org.gnome.Shell.Screenshot

Same reasoning applied to the layer-shell protocol: that interface is defined upstream and is not ours to add methods to. This one is exported on the same bus name and the same object path (/org/gnome/Shell/Screenshot), so a caller needs no second lookup — just a different interface name on the same object. phosh already ships io.furios.Flashlightd.xml, so the namespace is not new here.

If you would rather it sat directly on org.gnome.Shell.Screenshot, it is a one-line move in the XML and the codegen entry.

Why the schema stays here

io.furios.phosh.shell is phosh's schema and a second package cannot extend it, so the keys cannot travel with the plugins. They are also read by the Settings panel (FuriLabs/gnome-control-center#5) whether or not the plugin package is installed.

Note on the power button

This adds a screenshot path; it does not replace one. src/power-menu-manager.c is untouched on every branch in this series and the power-button screenshot works exactly as before.

Pairs with FuriLabs/phoc#2: the Show Touches option writes phoc's touch-points key and is inert until that lands.
Needed by furios-phosh-plugins#2, which cannot build until this is merged and libphosh-0.45-dev rebuilt from it.

5 commits, off forky. Builds clean on an FLX1.

[wayne-tbl]

ScreenshotDelayed now exercised on hardware. Returns immediately, the shell-owned timer survives the caller and fires, valid 1080x2416 PNG written.

The first attempt failed against a blanked screen and exposed an upstream defect: maybe_screencopy_done() completes the D-Bus invocation with no NULL guard and returns without disposing self->frames, so any failed screenshot refuses every later one until phosh restarts. That code is byte-identical to forky, so it does not come from this branch. Fixed in #7.