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>

LIFECYCLE-DESIGN.md

@@ -2,8 +2,8 @@
 
 > **Status: LC0–LC1 shipped; LC2–LC6 are design.** The structural attach/detach
 > pair and `@OnDetach` (§4, LC0), and reason-carrying `@OnDespawn` (§5, LC1), are
-> implemented and tested ([`examples/detach.ludic`](examples/detach.ludic),
-> [`examples/reason.ludic`](examples/reason.ludic), `bin/x test` checks). The
+> implemented and tested ([`examples/lang/detach.ludic`](examples/lang/detach.ludic),
+> [`examples/lang/reason.ludic`](examples/lang/reason.ludic), `bin/x test` checks). The
 > extensions LC2–LC6 are research-informed proposals, not built. This document
 > distills a survey of lifecycle models across seven systems (§3) into a roadmap
 > for Ludic. §13 lists the open decisions.
@@ -121,7 +121,7 @@ Lowering: `attach` guards on the has-flag and, when absent, reuses the existing
 `emit_init_component` (seed + `@OnAttach`); `detach` guards on presence, clears the
 flag, and fires `@OnDetach` with the property bound by name — the same binding the
 `@OnDisable` path already uses. No new runtime; POD data stays in `@S_` storage.
-See [`examples/detach.ludic`](examples/detach.ludic).
+See [`examples/lang/detach.ludic`](examples/lang/detach.ludic).
 
 ---
 
@@ -166,7 +166,7 @@ survey promises. The despawn hook compiles to `@on_despawn_<Model>(i32 %e, i32
 works without a user declaration; a user enum of the same name still shadows it.
 Backward-compatible: the `reason:` binding is optional, and `@OnDespawn` without
 it is unchanged. `@OnDetach` and scene `on exit` do **not** yet take reasons
-(§13.1). See [`examples/reason.ludic`](examples/reason.ludic).
+(§13.1). See [`examples/lang/reason.ludic`](examples/lang/reason.ludic).
 
 ---