ludic ui-preview: ludic.ui components previewed for a studio over stdio (R5)

A prebuilt tool, bin/ludic-ui-preview (built by ludic-dev build, shipped beside ludic-lsp, run as
`ludic ui-preview [--font DIR]`): ludic.ui with a backend that records every draw call as a line,
and mock component classes the studio describes (load / model / calls). frame t runs ui_show at
interface time t; text is measured on the CPU with the game's font.json metrics; locale goes
through ludic.i18n; tree / box / rules inspect the frame. No game code, no GPU, no network. The wire
protocol is frozen as tools/ui-preview/protocol-v1.md; smoke.txt is a transcript to run.

ludic.ui gains, all additive: UiClass.make_of, UiBackend.said / emitted, UiRule.text / at (with
comment line breaks kept so rule lines count true, and a class's styles read under its .lss path),
and ui_root, ui_find, ui_rules_of, ui_rule_value, ui_building, ui_class, ui_class_load,
ui_file_forget, ui_errors_clear; ui_nine_cuts_into exported.

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

tools/ui-preview/num.ludic

@@ -0,0 +1,59 @@
+# num.ludic - numbers and colours written into the reply: a space, then the number
+# a whole number, in decimal
+function pv_int(o: PvOut, n: int) -> void {
+  pv_byte(o, 32)
+  pv_digits(o, n)
+}
+function pv_digits(o: PvOut, n0: int) -> void {
+  var n = n0
+  if n < 0 {
+    pv_byte(o, 45)
+    n = 0 - n
+  }
+  if n >= 10 { pv_digits(o, n / 10) }
+  pv_byte(o, 48 + n % 10)
+}
+# a real number rounded to thousandths, with no trailing zeros: 12, 12.5, -0.125
+function pv_num(o: PvOut, x: float) -> void {
+  pv_byte(o, 32)
+  var a = x
+  var neg = false
+  if a < 0.0 {
+    a = 0.0 - a
+    neg = true
+  }
+  if a > 2000000.0 {                 # past what thousandths hold in an int: whole units
+    if neg { pv_byte(o, 45) }
+    pv_digits(o, int(a))
+    return
+  }
+  let c = int(a * 1000.0 + 0.5)
+  if neg and c != 0 { pv_byte(o, 45) }
+  pv_digits(o, c / 1000)
+  var f = c % 1000
+  if f == 0 { return }
+  pv_byte(o, 46)
+  var d = 100
+  while f > 0 {
+    pv_byte(o, 48 + f / d)
+    f = f % d
+    d = d / 10
+  }
+}
+# a colour, 0xRRGGBB, as #rrggbb (lower case); a negative (none, inherit) is #000000
+function pv_hex(o: PvOut, c0: int) -> void {
+  pv_byte(o, 32)
+  pv_byte(o, 35)
+  var c = c0
+  if c < 0 { c = 0 }
+  var shift = 1048576
+  for i in 0 .. 6 {
+    pv_byte(o, pv_hexch((c / shift) % 16))
+    shift = shift / 16
+  }
+}
+# a colour and its alpha, as every primitive and style line carries them
+function pv_rgba(o: PvOut, c: int, a: float) -> void {
+  pv_hex(o, c)
+  pv_num(o, a)
+}