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/README.md

@@ -0,0 +1,67 @@
+# Ludic documentation generator
+
+Generates the public documentation site (the `pages` branch) from a single
+source of truth, so the site can never drift from the language.
+
+## Source of truth
+
+```
+docs/
+  language/<category>/<id>.md    one file per symbol — keyword, type, builtin,
+                                 namespace method, operator, annotation
+  language/<category>/_section.md   section title + blurb + order
+  language/colors/palette.json   the 221 named colors (generated by palette.py)
+  site/site.json                 landing-page messaging (hero, features, …)
+  site/snippets/*.ludic          the code shown on the landing page (real programs)
+```
+
+### A symbol file
+
+```markdown
+---
+id: kw-handler            # anchor in api.html (kw-*, type-*, fn-*, <ns>-*, op-*, annot-*)
+name: handler             # display name / heading
+category: control         # which section (matches the directory)
+kind: keyword             # keyword | type | phase | namespace-method | builtin | annotation | operator
+tokens: handler           # the literal token(s) the highlighter recognizes & links
+sig: handler Name phase P { … }
+tip: A block that runs each frame in a given phase.   # one-line hover tip
+order: 3
+---
+
+Full description — inline HTML (`<code>`, `<b>`) and `backtick code` both work.
+
+```ludic
+handler Move phase Update { … }
+```
+```
+
+Add such a file and it appears in the API Reference, is recognized + tipped +
+linked in **every** code snippet across the site, and lands in `symbols.json` —
+with no other file to edit.
+
+## Build
+
+```bash
+python3 tools/docgen/gen.py --out build/pages   # generate the whole site
+python3 tools/docgen/check.py build/pages        # sanity-check before publish
+```
+
+Outputs into `--out`: `index.html`, `api.html`, `ludic-highlight.js`
+(its symbol tables generated from the sources above), `symbols.json`, `.nojekyll`.
+
+No third-party dependencies — Python standard library only.
+
+## Publish
+
+`.forgejo/workflows/docs.yml` runs this on every push to `main` that touches
+`docs/**` or `tools/docgen/**`, and force-publishes the result to the `pages`
+branch root (which the pages-server serves). It needs a repo secret
+`PAGES_TOKEN` with write access (or the automatic Actions token enabled for
+pushes). `index.html` + `.nojekyll` always stay at the branch root.
+
+## Colors
+
+`palette.json` is generated by `tools/docgen/palette.py` from a single `PALETTE`
+table, which also generates `selfhost/emit_color.ludic`. Regenerate colors
+there; never hand-edit either output.