feat(lang): UI components as files - component Name { ... } beside Name.xml and Name.lss

The compiler turns a component declaration into:
- a record of its props and state;
- a constructor, a props setter, a model and a call;
- a class, registered with ludic.ui at start.

Its template and styles are read from beside it and compiled in, with @import inlined, and a
missing template fails the build.

In the runtime:
- each mounted instance keeps its own props and state, and `set` in a template writes the state;
- styles are scoped to the component;
- class, style and id on a component's tag land on its root, styled by the parent's sheet too;
- ui_reload re-reads a component's files from disk and keeps instances.

The package's own module is now ludic_ui, so a program may call a directory of its own ui.

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

packages/ludic.ui/reload.ludic

@@ -2,12 +2,17 @@
 # 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
+  var changed = uc_reload()
   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 }
+  ui_errs = new []string
+  if len(lib_files) == 0 {
+    print(`ui: templates reloaded`)
+    return true
+  }
   let old = lib_files
   lib_files = new []UiFile
   lib_screen_names = new []string
@@ -22,6 +27,7 @@ export function ui_reload() -> bool {
     if have { continue }
     if f.disk { lib_file(f.path) } else { ui_load_text(f.src, f.path) }
   }
+  uc_invalidate()
   print(`ui: templates reloaded`)
   return true
 }