feat(ui): ludic.ui grows toward HTML, CSS and React (Phase 0.U1-U4)

- Natives: ui_native(tag, measure, draw) makes an element the program draws itself; ui_fire
  runs its on-<event> with event.value. input, select and textarea have simple defaults.
- React:
  - keyed <each>, <let>, <provide> context through components, <fragment>;
  - named slots, default props on <component>;
  - on-mount / on-unmount;
  - inline text inside text elements.
- CSS:
  - custom properties and var();
  - position relative/absolute/fixed with insets and z-index;
  - em/rem/vw/vh and @media;
  - wrapping text and ellipsis, overflow;
  - + and ~ combinators, :nth-child(an+b), :checked, :active.
- Developing: errors with file:line, ui_errors(), ui_reload() keeping state, and an
  inspector-style ui_dump.
- view fields infer the type of a literal or a named function's result.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

packages/ludic.ui/reload.ludic

@@ -0,0 +1,27 @@
+# reload.ludic - a developer's templates and stylesheets read again when they change on disk: every
+# file is re-read in the order it was first loaded (so an import is there before its importer), and
+# the screens' state is kept, as React's fast refresh keeps it. True when anything changed.
+export function ui_reload() -> bool {
+  var changed = false
+  for i in 0 .. len(lib_files) {
+    let f = lib_files[i]
+    if f.disk and lib_text(f.path) != f.src { changed = true }
+  }
+  if not changed { return false }
+  let old = lib_files
+  lib_files = new []UiFile
+  lib_screen_names = new []string
+  lib_screens = new []UiTpl
+  ui_errs = new []string
+  for i in 0 .. len(old) {
+    let f = old[i]
+    var have = false
+    for k in 0 .. len(lib_files) {
+      if lib_files[k].path == f.path { have = true }
+    }
+    if have { continue }
+    if f.disk { lib_file(f.path) } else { ui_load_text(f.src, f.path) }
+  }
+  print(`ui: templates reloaded`)
+  return true
+}