refactor(lang): rename the str type (and stringify builtin) to string

Expand the abbreviated string type and its conversion builtin to the full
word everywhere:
  str            ->  string        (the immutable-string type)
  str(x) -> str  ->  string(x) -> string   (the stringify builtin;
                                            what `{…}` interpolation calls)

Types are recognized by identifier, and llty maps both spellings to LLVM
`ptr`, so this is an atomic source rewrite: type annotations, the Ludic
type tags, the builtin name/dispatch, and the interpolation desugar, plus
the grammars, LSP, docs (type-str -> type-string, fn-str -> fn-string), and
inventory. int/bool stay (universally accepted, like Math).

Reseeded; C-free fixpoint holds; all suites green (45/24/29); site + check.py OK.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

docs/language/text/text-from_int.md

@@ -4,14 +4,14 @@ name: Text.from_int
 category: text
 kind: namespace-method
 tokens: Text.from_int
-sig: Text.from_int(n) -> str
+sig: Text.from_int(n) -> string
 tip: Render an integer as a string.
 order: 10
 ns: Text
 member: from_int
 ---
 
-Returns the decimal text of the integer <code>n</code> — <code>Text.from_int(1234)</code> is <code>"1234"</code>, and negatives keep their sign. It is the same conversion as the bare <code>str(n)</code> and the inverse of <code>Text.to_int</code>. Use it when you need a number as characters — to measure its width, concatenate it, or store it — though drawing a number to the screen is better done with <code>Screen.draw_number</code>.
+Returns the decimal text of the integer <code>n</code> — <code>Text.from_int(1234)</code> is <code>"1234"</code>, and negatives keep their sign. It is the same conversion as the bare <code>string(n)</code> and the inverse of <code>Text.to_int</code>. Use it when you need a number as characters — to measure its width, concatenate it, or store it — though drawing a number to the screen is better done with <code>Screen.draw_number</code>.
 
 Parameters:
 - `n` — the integer to render