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/tpl.ludic

@@ -10,29 +10,12 @@ export property UiTpl {
   text: UiExpr = null
   kids: []UiTpl = null
   comp: UiTpl = null            # the component this tag names, found when its file loads
+  cls: UiClass = null           # or the Ludic-declared component it names
   sheet: UiSheet = null         # the styles of the file it was written in
   style: UiRule = null          # its style="..." attribute, read as declarations
   raw: string = ""              # a <style>'s text, which is not a template's
   where: string = ""            # file:line, for an error
 }
-# the text being read, and where its lines start, so an element can say which line it is on
-var tp_nl: []int = new []int
-function tp_lines(src: string) -> void {
-  tp_nl = new []int
-  for i in 0 .. len(src) {
-    if src[i] == 10 { push(tp_nl, i) }
-  }
-}
-function tp_line(at: int) -> int {
-  var lo = 0
-  var hi = len(tp_nl)
-  while lo < hi {
-    let mid = (lo + hi) / 2
-    if tp_nl[mid] < at { lo = mid + 1 } else { hi = mid }
-  }
-  return lo + 1
-}
-
 function tpl_read(x: Xml, file: string) -> UiTpl {
   let t = new UiTpl
   t.tag = Xml.tag(x)