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/instance.ludic

@@ -0,0 +1,35 @@
+# instance.ludic - a mounted component's record (its props and state), found by where it sits in the
+# tree; one that a build of its screen did not reach is gone, and its state with it
+property UiInst {
+  key: string = ""
+  cls: UiClass = null
+  ptr: pointer = null
+  seen: int = 0
+}
+var in_list: []UiInst = new []UiInst
+var in_build: int = 0
+function in_get(key: string, k: UiClass) -> UiInst {
+  for i in 0 .. len(in_list) {
+    let it = in_list[i]
+    if it.key == key and it.cls.name == k.name {
+      it.seen = in_build
+      return it
+    }
+  }
+  let it = new UiInst
+  it.key = key
+  it.cls = k
+  it.ptr = k.make()
+  it.seen = in_build
+  push(in_list, it)
+  return it
+}
+# after a build of `screen`: its instances the build did not reach are unmounted
+function in_sweep(screen: string) -> void {
+  let keep = new []UiInst
+  for i in 0 .. len(in_list) {
+    let it = in_list[i]
+    if it.seen == in_build or not lc_mine(it.key, screen) { push(keep, it) }
+  }
+  in_list = keep
+}