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>

docs/site/site.json

@@ -79,7 +79,7 @@
     "intro": "Build the toolchain once, then your game. Everything runs from the repo root.",
     "steps": [
       { "title": "Build the toolchain", "html": "<code>bin/x build</code> produces <code>ludicc</code>, the compiler you'll use for everything below." },
-      { "title": "Compile &amp; run an example", "html": "<code>bin/x app examples/snake.ludic</code> turns a <code>.ludic</code> file into a native binary. Run it to open a real window." },
+      { "title": "Compile &amp; run an example", "html": "<code>bin/x app examples/games/snake.ludic</code> turns a <code>.ludic</code> file into a native binary. Run it to open a real window." },
       { "title": "Go headless for tests", "html": "<code>--headless</code> renders frames to a <code>.ppm</code> from piped input — deterministic output you can diff." },
       { "title": "Edit with full tooling", "html": "<code>bin/x tools</code> builds the formatter and language server; every editor gets completion, diagnostics and go-to-definition." }
     ],
@@ -89,11 +89,11 @@
       { "cmd": "bin/x build" },
       { "blank": true },
       { "comment": "build and run an example (opens a window)" },
-      { "cmd": "bin/x app examples/snake.ludic" },
+      { "cmd": "bin/x app examples/games/snake.ludic" },
       { "cmd": "./build/snake" },
       { "blank": true },
       { "comment": "deterministic headless render for tests" },
-      { "cmd": "bin/x app examples/snake.ludic --headless" },
+      { "cmd": "bin/x app examples/games/snake.ludic --headless" },
       { "cmd": "printf 'ddddwww' | ./build/snake_headless" },
       { "out": "→ writes out.ppm" }
     ]