Port · Parity: every page matches gpui 0.2.2's; the rules re-tested

Every page and scripted state was shot with gpui 0.2.2 and with the
port, light and dark, full width and at 280px, judged pair by pair by
agents with skeptics, and every page's log diffed. What differed is
fixed, each with a test that fails without it where the test platform
can show it:

- The gallery's harness takes posted mouse moves (gpui_macos listens
  to a tracking area), posts each drag move twice (it no longer
  replays a held drag), and waits three frames before each shot.
- Rolling digits: a block column, so taffy 0.13 lends the cell no
  baseline, and a line of whole device pixels, since gpui snaps each
  length on its own. DescriptionList's row aligns ends.
- Margins that taffy 0.13 collapses through a plain block: the
  drawer's pull and snap, the stagger and transition rise, the dialog
  and palette rises, the fullscreen dialog's slide.
- An Input keeps room to type in a squeezed row; the field rows drop
  w_full, whose reason was taffy 0.9's.

AGENTS.md's rules that named gpui 0.2.2 or taffy 0.9 were re-tested
against both sources and rewritten, and new ones say what the port
changed. TASKS.md's tags follow: what the new gpui makes possible is
prove. Captions, doc comments and README say what holds now.

README.md

@@ -10,15 +10,16 @@ Status: early. `TASKS.md` tracks every component, chapter by chapter.
 ```toml
 [dependencies]
 ely-gpui-component = { git = "https://github.com/ZacharyZhang-NY/Ely-GPUI-Components" }
-gpui = "0.2.2"
+gpui = { git = "https://github.com/zed-industries/zed", rev = "1a28cff4b409169bac058bca40dfbfeb7621d19b" }
+gpui_platform = { git = "https://github.com/zed-industries/zed", rev = "1a28cff4b409169bac058bca40dfbfeb7621d19b", features = ["font-kit"] }
 ```
 
 ```rust
 use ely_gpui_component::{Assets, theme::{Mode, Theme}};
-use gpui::{App, Application};
+use gpui::App;
 
 fn main() {
-    Application::new().with_assets(Assets).run(|cx: &mut App| {
+    gpui_platform::application().with_assets(Assets).run(|cx: &mut App| {
         ely_gpui_component::init(cx);
         Theme::set_mode(Mode::Dark, cx);
     });
@@ -37,7 +38,7 @@ cargo run --example gallery -- --capture shots   # macOS: PNG of every page, lig
 
 ## Build notes
 
-- gpui 0.2.2 compiles its Metal shaders at runtime here (`runtime_shaders`, on by default), so a full Xcode install is not required.
+- gpui compiles its Metal shaders at runtime here (`runtime_shaders`, on by default), so a full Xcode install is not required. gpui_platform needs `font-kit`, or macOS draws no text.
 - Tested on macOS only. The capture tool needs macOS.
 
 ## License