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>

packages/ludic.ui/backend.ludic

@@ -20,6 +20,8 @@ export property UiBackend {
   read: fn(string) -> string = null        # a template file's text (else Fs.read_text)
   now: fn() -> float = null                # seconds, for animation (else frames at 60 a second)
   input: bool = true               # false: take no input from Input.* (a test drives it)
+  said: fn(string) -> void = null          # a template error, for a host that reports it itself (else printed)
+  emitted: fn(string) -> void = null       # `emit name` ran, whether or not a handler took it (a host's log)
 }
 # a renderer a program installs by importing it (render3d.ludic): the first one is the backend
 property UiRenderer {