feat(ui): number and key fields, notes, anchored popovers, text-shadow, and pictures as painted

- <input type="number" min max step>: typed digits replace its value (a minus when min allows one,
  a point when step has a fraction), Enter or leaving the field commits them held between min and
  max, the left and right arrows step it.
- <input type="key">: Enter or a click starts it listening and the next key is its value, Tab, the
  arrows and Enter included; Esc stops it listening, Backspace clears it, `shown` names the value,
  and ui_capturing() tells the host to leave its keys alone (through the frame that ended it).
- note="..." under any control's label (.ui-labels > .ui-label + .ui-note); a range's (or number's)
  value with decimals, format="percent" and a unit.
- A popover with `anchor="id"` (the nearest element of that id) or a bare `anchor` (the element
  before it) sits beside it by `placement` (right, left, bottom, top), its margin the gap, opens to
  the other side where it would leave the screen, and is kept on it.
- A tooltip's title splits into lines at a newline or a written \n.
- text-shadow, inherited, drawn sharp under the text.
- ui_opacity(): the group opacity a native's draw is at.
- border-image is drawn as painted with no background colour, tinted by one, and not at all when
  that colour is transparent (it drew a white nine-slice).
- A picture file is drawn untinted, as a browser draws one; an atlas cell (prefix:name) still takes
  the color around it, and an <img> with its own color is tinted by it.
- The render3d backend loads a picture again when its file changes or appears (a failed load was
  kept for ever), and at once after ui_image_reload(path); takes a path with a drive letter (C:/...)
  as a path rather than an atlas; and slices a nine-slice by its texture's own width and height.
- ui_inputs.ludic and ui_look.ludic; LANGUAGE.md and the changeset say all of it.

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

examples/library/ui_inputs_parts/Form.lss

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+.page { width: 400px; gap: 4px }
+input { width: fill }

examples/library/ui_inputs_parts/Form.ludic

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+# Form.ludic - a number, a key binding, two ranges with their values formatted, a note under a label,
+# and an event called set
+component Form {
+  state count: int = 5
+  state bind: int = 32
+  state vol: float = 0.5
+  state said: int = 0
+  on set(v: int) { said = v }
+}

examples/library/ui_inputs_parts/Form.xml

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+<div class="page">
+  <input type="number" label="Count" note="How many to carry" min="{0}" max="{20}" value="{count}" on-change="set count = event.value"/>
+  <input type="key" label="Jump" value="{bind}" shown="{bind == 32 ? 'Space bar' : ''}" on-change="set bind = event.value"/>
+  <input type="range" label="Volume" min="{0}" max="{1}" step="{0.1}" value="{vol}" format="percent" on-change="set vol = event.value"/>
+  <input type="range" label="Delay" min="{0}" max="{2}" step="{0.25}" value="{0.5}" decimals="{2}" unit=" s"/>
+  <button on-click="set(9)">Nine</button>
+  <Tag text="{7}"/>
+  <p>{count} {bind} {vol} {said}</p>
+</div>

examples/library/ui_inputs_parts/Tag.ludic

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+# Tag.ludic - a string prop, which a number given to it arrives in as text
+component Tag {
+  prop text: string = "none"
+}

examples/library/ui_inputs_parts/Tag.xml

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+<p>{text}!</p>