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/ecs/world_get.ludic

@@ -0,0 +1,22 @@
+# world_get.ludic — EV2 reflection: read and write a component by NAME through the
+# world table, driven from Ludic (replaces tests/mod_c/world_mod.c). world_prop_id
+# / world_field_id resolve names to ids; world_get / world_set / world_has read and
+# write by those ids — the same reflection ABI a foreign mod binds, now callable
+# from Ludic. Spawns a Unit (Init sets hp=max=50), then reads/tests/writes hp.
+# Prints 50 / 1 / 7.
+program WorldGet {
+  property Health { hp: int = 0, max: int = 0 }
+  model Unit { Health }
+  @Public @OnSpawn(Unit) handler Init { Health.hp = Health.max }   # -> emits the world table
+
+  entry {
+    spawn Unit { Health { max: 50 } }
+    let H  = world_prop_id("Health")
+    let hp = world_field_id(H, "hp")
+    let e  = world_query_next(H, 0)
+    print(world_get(e, H, hp))      # 50 — read by name
+    print(world_has(e, H))          # 1  — entity has Health
+    world_set(e, H, hp, 7)          # write by name
+    print(world_get(e, H, hp))      # 7  — the write stuck
+  }
+}