chore(repo): DX cleanup — categorise examples, text-diffable golden, build/ output (#27 #28 #30)

Repository-cleanup / DX pass folding three tracker items into one coherent
change, verified green end to end (`bin/x test` 49/0, `bin/x selfhost-test`
29/0, `bin/x test-tools` 29/0).

#28 — curate & categorise examples/
- 42 flat entries regrouped into intent-revealing subdirs: games/, rendering/,
  ecs/, events/, networking/, lang/, library/ (was lib/).
- chronorift dir-vs-file duplication resolved: the entry file and its import
  modules now live together under games/chronorift(.ludic).
- Every path reference updated repo-wide (test runner, editor-tool drivers,
  docs/site, design docs).
- New examples/README.md indexes the whole set with run commands.
- Showcase examples without a self-asserting entry (hello, events, net_rt) now
  get a compile-only rot guard in `bin/x test`, so nothing here rots silently.

#30 — text-diffable golden baseline
- The 4 binary selfhost/golden/*.ppm blobs are replaced by a single
  selfhost/golden/renders.sha256 manifest (SHA-256 per render). Hashes are
  byte-identical to the old PPMs, so the baseline is unchanged — only its form.
- game_case now compares framebuffer hashes; a regression shows as a changed
  hex line in review, not "binary files differ".
- New `bin/x golden` regenerates the manifest deliberately (review with
  `git diff selfhost/golden/renders.sha256`).

#27 — PPM & asset handling
- Headless renders now write build/out.ppm, never the repo root; `x app`,
  `x clean`, messaging and .gitignore updated to match. Nothing is written to
  the working root any more.
- Redundant local Kenney .zip archives removed (the art ships extracted;
  .gitignore already excludes *.zip). CC0 License.txt files retained.

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

tools/test-grammar.js

@@ -119,7 +119,7 @@ async function main() {
   expect('scene in enter', '  enter Battle', 'Battle', 'entity.name.type.scene');
 
   // A whole file must tokenise without the engine bailing out.
-  const sample = fs.readFileSync(path.join(ROOT, 'examples', 'menu.ludic'), 'utf8');
+  const sample = fs.readFileSync(path.join(ROOT, 'examples', 'games', 'menu.ludic'), 'utf8');
   let state = vsctm.INITIAL;
   let tokenCount = 0;
   for (const line of sample.split('\n')) {
@@ -127,8 +127,8 @@ async function main() {
     state = r.ruleStack;
     tokenCount += r.tokens.length;
   }
-  if (tokenCount > 200) ok(`tokenises examples/menu.ludic (${tokenCount} tokens)`);
-  else bad('tokenises examples/menu.ludic', `only ${tokenCount} tokens`);
+  if (tokenCount > 200) ok(`tokenises examples/games/menu.ludic (${tokenCount} tokens)`);
+  else bad('tokenises examples/games/menu.ludic', `only ${tokenCount} tokens`);
 
   // ---- the Markdown injection ---------------------------------------------
   const mdGrammar = await registry.loadGrammar('markdown.ludic.codeblock');