Example repos that move with fizzy, and a dvui app on fizzy's backend #281

Fizzy's examples become two repos that move with fizzy, and the app one grows a plain dvui app on fizzy's backend. That dvui app is the proof that the windowing work belongs in dvui (#243).

• fizzyedit/example-app: fizzy as a library.
  • zig build run-fizzy -Dshape=minimal|studio|endless is a whole fizzy app in that shape.
  • zig build run-dvui will be dvui's own widgets on fizzy's backend: floats, menus and dialogs as OS windows, Liquid Glass on macOS.
• fizzyedit/example-plugin: the smallest plugin, the template to copy.

Moving with fizzy.

• Fizzy's CI builds both repos against each PR's own tree (scripts/check-examples.sh), fetched as a URL dependency would be.
• An SDK release asks example-plugin to repin, as it asks the store plugins.

Steps

• Both repos created, with the shapes, the hello plugin (now example-plugin) and the shader plugin (example-app's own).
• build: fizzy builds when fetched as a URL dependency #279: fizzy builds when fetched as a URL dependency. VERSION, app/ and web/ were missing from .paths.
• examples: moved to fizzyedit/example-app and example-plugin #282: fizzy's examples/ removed, with CI building the two repos instead (stacked on build: fizzy builds when fetched as a URL dependency #279).
• example-app repinned from build: fizzy builds when fetched as a URL dependency #279's commit to main once build: fizzy builds when fetched as a URL dependency #279 merges (replay: the replay app moves here; fizzy pinned at main with the cold-cache fix example-app#2), and again to main with the backend package and SDK 0.2.20 (build: pin fizzy at main with its backend package, SDK 0.2.20 example-app#3).
• PLUGIN_DISPATCH_TOKEN scoped to example-plugin too, so the SDK release's repin request reaches it (a repo setting). At 0.2.20 every repin request, to the store plugins too, got HTTP 403: the token reaches none of them.
• example-app follows fizzy main on its own: a workflow that repins it when fizzy releases.
• backend: fizzy's native backend is a package of its own #312: fizzy's backend as a package of its own (Windowing foundation: one model, decided once a frame, tested without a screen #243's "On fizzy's side"): SDLBackend, GpuRenderer, platform/**, viewport_map, the SDL pin.
• Popout's generic half moves into it: subwindows, dialogs and menus into OS windows, driven by dvui's drawRetained and screensSet (popout: dialogs drawn through dvui's drawRetained, not drawEarly #278).
  • backend: the viewports API is the backend package's, with a stand-in #324: the viewports API is the package's, with a stand-in (viewports_none) for backends without OS windows; build: fizzy builds on dvui's SDL3 backend again, and CI keeps it #328 makes -Dnative-backend=sdl3 build again.
  • backend: viewports.Picture, fizzy.addDvui, the pointer over OS windows #326: one way to draw a viewport's picture, viewports.Picture (stacked on backend: the viewports API is the backend package's, with a stand-in #324).
  • build: a dvui app of its own on fizzy's backend (fizzy.addDvui) #329: fizzy.addDvui, a dvui app of its own on fizzy's backend or dvui's (stacked on backend: viewports.Picture, fizzy.addDvui, the pointer over OS windows #326).
  • popout: a demo's pointer shows over float, menu and dialog windows #330: a demo's pointer shows over float, menu and dialog windows (stacked on backend: viewports.Picture, fizzy.addDvui, the pointer over OS windows #326).
• core: floats' screens are dvui's (dvui.screensSet) #325: fizzy adopts dvui.screensSet in place of core.screens' dvui-data plumbing.
• example-app's run-dvui: a plain dvui app on that backend. Its floating windows are OS windows (dvui: run-dvui, dvui's demo and floating windows as OS windows example-app#4, draft until build: a dvui app of its own on fizzy's backend (fizzy.addDvui) #329 lands); menus and dialogs later, once the app can say which subwindows are menus.
• The two dvui changes proposed upstream (foxnne/dvui-dev branches window-draw-retained, screens-set), with run-dvui as the demonstration.