docs: automated documentation pipeline (per-symbol source → pages)

Replace the hardcoded landing page and minimal reference with a generated
documentation site driven by a single source of truth.

- docs/language/**: one file per symbol (93 keywords/types/builtins/namespace
  methods/operators/annotations), each with front-matter (id, kind, tokens,
  sig, tip) + description + a ```ludic example. Seeded by exploding the former
  inline SECTIONS list; these files are now the source of truth.
- docs/site/: site.json (editable hero/features/showcase/messaging, not
  hardcoded) + snippets/*.ludic (real programs shown on the landing page).
- tools/docgen/gen.py: generates index.html, api.html, ludic-highlight.js and
  symbols.json. The highlighter's symbol tables, hover tips and jump anchors
  are GENERATED from the per-symbol files — add a symbol and it is recognized,
  tipped and linked in every snippet automatically. Python stdlib only.
- tools/docgen/check.py: verifies the pages contract + that no snippet token
  links to a missing reference anchor.
- .forgejo/workflows/docs.yml: rebuilds and publishes to the pages branch on
  every push to main touching the docs sources.

Consumes the new Screen.*/Color.*/named-arg API and the 221-color palette.

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

tools/docgen/check.py

@@ -0,0 +1,41 @@
+#!/usr/bin/env python3
+"""check.py — sanity-check a generated docs site before it is published.
+
+Verifies:
+  * the pages-server contract: index.html + .nojekyll exist at the root;
+  * api.html and ludic-highlight.js are present;
+  * every anchor the highlighter links to actually exists in api.html
+    (so no code-snippet token points at a missing entry).
+
+Usage: python3 tools/docgen/check.py <site-dir>
+Exit code 1 on any failure.
+"""
+import json, os, re, sys
+
+def main(site):
+    problems = []
+    need = ["index.html", "api.html", "ludic-highlight.js", ".nojekyll", "symbols.json"]
+    for f in need:
+        if not os.path.exists(os.path.join(site, f)):
+            problems.append(f"missing required file: {f}")
+    if os.path.exists(os.path.join(site, "symbols.json")) and os.path.exists(os.path.join(site, "api.html")):
+        sym = json.load(open(os.path.join(site, "symbols.json")))
+        ids = set(re.findall(r'id="([^"]+)"', open(os.path.join(site, "api.html")).read()))
+        anchors = set()
+        for grp in ("keywords", "types", "phases", "builtins", "nsmethods", "annotations"):
+            anchors |= set(sym.get(grp, {}).values())
+        anchors.add(sym.get("colors_anchor", "colors"))
+        anchors.add(sym.get("annotations_anchor", "annotations"))
+        for a in sorted(anchors):
+            if a not in ids:
+                problems.append(f"highlighter links to #{a} but api.html has no such anchor")
+    if problems:
+        print("docs check FAILED:")
+        for p in problems:
+            print("  -", p)
+        return 1
+    print("docs check OK:", site)
+    return 0
+
+if __name__ == "__main__":
+    sys.exit(main(sys.argv[1] if len(sys.argv) > 1 else "build/pages"))