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>

examples/events/promote.ludic

@@ -0,0 +1,32 @@
+# promote.ludic — EV1: `@Public` promotes a lifecycle hook to a public event.
+#
+# Marking a lifecycle hook `@Public` makes its fire site ALSO emit an event named
+# for the moment — `model_<M>_spawn`, `model_<M>_despawn` — carrying the entity
+# (and, for despawn, the EndReason). Anything can then subscribe: a native
+# listener with `@On(model_Enemy_spawn)`, or a foreign mod binding
+# `ludic_on_model_Enemy_spawn` over the C ABI. The game's own lifecycle becomes
+# the modding surface, with no hand-written `emit` in the hook body.
+#
+# Running it prints:  100 101 200 201
+program Promote {
+  property Health { hp: int = 0, max: int = 100 }
+  model Enemy { Health }
+
+  @Public @OnSpawn(Enemy)   handler Init  { Health.hp = Health.max }   # -> model_Enemy_spawn
+  @Public @OnDespawn(Enemy) handler Clean { }                          # -> model_Enemy_despawn
+
+  # Listeners on the promoted events. These read the generated payload (entity,
+  # and reason for despawn) by name — exactly what a foreign mod receives.
+  @On(model_Enemy_spawn)   handler Spawned { print(entity + 100) }
+  @On(model_Enemy_despawn) handler Died    { print(entity + reason + 200) }
+
+  handler Seed phase Start {
+    spawn Enemy { Health { max: 50 } }     # entity 0 -> Spawned 100
+    spawn Enemy { Health { max: 60 } }     # entity 1 -> Spawned 101
+  }
+
+  handler Run phase Update {
+    for (h) in query [Health] { despawn self() }   # despawn 0 -> Died 200, despawn 1 -> Died 201
+    quit()
+  }
+}