docs: correct stale references across LANGUAGE, README, COMPILING, CONTRIBUTING

- LANGUAGE.md: real diagnostic format, list literals, Font.load / Ui.*
  (no `reg`/`set_reg`, no `/Handler/Library` typo), `extern function`,
  existing example links, Input.key(); builtins table trimmed to what exists
- COMPILING.md: pipeline names selfhost/ (not compiler/*.c), `program`
  instead of game/module, all thirteen win_* entry points by group
- README.md: the window seam is not "five" functions
- CONTRIBUTING.md: docs are checked with `x docs-gen` / `x docs-check`
- docs/language: kw-ui and fn-ui_build use the namespaced API;
  @ClearColor documents constant expressions; examples/README lists
  operators.ludic

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

README.md

@@ -15,8 +15,9 @@ with **no C compiler in the loop**.
 **No C is generated, compiled or linked in a build.** No interpreter, no
 transpiler, no C runtime: the framebuffer, sprites, PNG/DEFLATE decoding,
 TrueType text, the retained UI, the registers and the RNG are all written in
-Ludic (`runtime/native/*.ludic`); only the window seam — five `win_*` functions
-— is hand-written LLVM IR against the platform ABI (`runtime/native/cocoa.ll`),
+Ludic (`runtime/native/*.ludic`); only the window seam — the `win_*` functions
+for the window, keys, mouse, cursor, gamepad and touch — is hand-written LLVM IR
+against the platform ABI (`runtime/native/cocoa.ll`),
 the same floor Rust and Swift stand on.
 
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