feat(ui): popovers, tooltips, progress; the render3d backend installs itself; duplicate names caught first

- `popover`: a top layer that keeps the pointer and the keyboard, closed by a press outside or Esc.
- `title` tooltips after half a second's rest, styled by .ui-tooltip.
- `<progress>` and `<meter>`.
- Atlases take rows and number cells, and importing ludic.ui/render3d.ludic is enough to draw with
  render3d.
- The compiler reports two declarations of one name before it type-checks, so a package global
  clashing with a program's reads as that, not as 29 type errors.

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

examples/library/ui_popover.ludic

@@ -0,0 +1,59 @@
+# ui_popover.ludic — HTML's popover and progress in ludic.ui: a button opens a popover of verbs, the
+# keyboard stays inside it, a press outside or Esc closes it, and a progress bar fills to its value.
+import "ludic.ui"
+import "ui_popover_parts/Verbs.ludic"
+program UiPopover {
+  numbers float
+  function frame(i: UiInput) -> UiNode {
+    ui_input(i)
+    ui_show("Verbs", null, 0.0, 0.0, 400.0, 400.0)
+    let root: UiNode = ui_nodes("Verbs", null)
+    ui_place(root, 0.0, 0.0, 400.0, 400.0)
+    return root
+  }
+  function click(x: float, y: float) -> void {
+    let d = new UiInput
+    d.x = x
+    d.y = y
+    d.down = true
+    frame(d)
+    let u = new UiInput
+    u.x = x
+    u.y = y
+    frame(u)
+  }
+  function said(root: UiNode) -> string {
+    let page = root.children[0]
+    return page.children[len(page.children) - 1].text
+  }
+  entry {
+    ui_backend(new UiBackend)
+    var root = frame(new UiInput)
+    let cell = root.children[0].children[0]
+    click(cell.x + 2.0, cell.y + 2.0)
+    root = frame(new UiInput)
+    let tab = new UiInput
+    tab.tab = true
+    frame(tab)
+    frame(tab)
+    root = frame(tab)
+    let enter = new UiInput
+    enter.enter = true
+    root = frame(enter)
+    root = frame(new UiInput)
+    let first = said(root)
+    click(cell.x + 2.0, cell.y + 2.0)
+    root = frame(new UiInput)
+    let opened = said(root)
+    click(390.0, 390.0)
+    root = frame(new UiInput)
+    let outside = said(root)
+    click(cell.x + 2.0, cell.y + 2.0)
+    let esc = new UiInput
+    esc.escape = true
+    frame(esc)
+    root = frame(new UiInput)
+    let bar = root.children[0].children[1]
+    print(`{first} | {opened} | {outside} | {said(root)} | fill {int(bar.children[0].cw)} of {int(bar.cw)}`)
+  }
+}