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/smoke.txt

@@ -0,0 +1,152 @@
+# smoke.txt - a scripted session for ludic ui-preview (protocol-v1.md), to be run by hand or by a
+# small driver: `bin/ludic-ui-preview < requests` where the requests are the `> ` lines below, in order.
+#
+#   > LINE     a request, sent as it stands (without the "> ")
+#   < TEXT     some reply line of that request contains TEXT (in order within the reply)
+#   <= LINE    the request's terminal line is exactly LINE
+#   <! TEXT    no reply line of that request contains TEXT
+#
+# No font is loaded, so a character measures half the font size, and the viewport is 1920 x 1080, so
+# a design pixel is a screen pixel and the default text is 16 px (a 4-letter word is 32 wide).
+
+> hello
+<= ok ui-preview 1 "" ""
+
+> viewport 1920 1080
+<= ok
+
+> native "dial" 40 40
+<= ok
+
+> load "Pill" "<row id=\"root\" class=\"pill\">\n  <p id=\"label\">{label}</p>\n  <p id=\"pct\">{pct(0)}</p>\n  <button id=\"go\" on-press=\"pick(3)\">Go</button>\n  <button id=\"set\" on-press=\"set n = 2\">Set</button>\n  <button id=\"close\" on-press=\"emit close\">Shut</button>\n  <dial id=\"d\"/>\n  <Badge id=\"badge\"/>\n</row>" ".pill {\n  background: #203040;\n  padding: 8;\n  gap: 4;\n}\np { color: #ff0000; }"
+<! err
+<= ok
+
+> model "Pill" {"label": "Food", "n": 0}
+<= ok
+
+> show Pill
+<= ok
+
+> frame 0
+< frame 0
+< rect
+< #203040 1
+< text
+< 16 32 #ff0000 1 "Food"
+< round
+< #3a3f46 1
+< "Go"
+< native "dial"
+< end
+< miss "Pill" "pct"
+<= ok
+
+> calls "Pill" {"pct": [80, 20], "pick": true}
+<= ok
+
+> frame 0.5
+< frame 0.5
+< "80"
+< end
+<! miss
+<= ok
+
+> input key tab
+<= ok
+
+> frame 1
+< end
+<= ok
+
+> input key enter
+<= ok
+
+> frame 1.1
+< end
+< call "Pill" "pick" [3]
+<= ok
+
+> input key tab
+<= ok
+
+> frame 1.2
+<= ok
+
+> input key enter
+<= ok
+
+> frame 1.3
+< set "Pill" "n" 2
+<= ok
+
+> input key tab
+<= ok
+
+> frame 1.4
+<= ok
+
+> input key enter
+<= ok
+
+> frame 1.5
+< emit "close"
+<= ok
+
+> load "Badge" "<span class=\"b\">new</span>" ".b { color: #00ff00; }"
+<= ok
+
+> frame 2
+< #00ff00 1 "new"
+<= ok
+
+> tree
+< node 0
+< "root"
+< "go"
+< "Food"
+<= ok
+
+> box label
+< box "
+< style font-size 16
+< style color #ff0000 1
+<= ok
+
+> rules label
+< rule "Pill.lss" 6
+< "p"
+< decl "color" "#ff0000"
+<= ok
+
+> box nosuch
+<= fail "box nosuch: no element has that id or key"
+
+> load "Bad" "<row>\n  <nosuch/>\n</row>" ""
+< err "Bad.xml" 2 0 "<nosuch>: there is no such element
+<= ok
+
+> atlas "icon" "icons" 4 2 ["tent", "fish"]
+<= ok
+
+> load "Pic" "<row><img src=\"icon:fish\"/><img src=\"photo.png\"/></row>" ""
+<= ok
+
+> show Pic
+<= ok
+
+> frame 3
+< image atlas "icons" 1
+< 0.25 0 0.5 0.5
+< image path "photo.png"
+< 0 0 1 1 #ffffff 1
+<= ok
+
+> frobnicate
+<= fail "unknown request frobnicate"
+
+>
+<= ok
+
+> quit
+<= ok