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.ludic

@@ -1,25 +0,0 @@
-# events.ludic — EV0: the event bus core.
-#
-# `event E { fields }` declares a public event carrying a POD payload. `@On(E)
-# handler …` registers a listener whose body reads the payload fields by name.
-# `emit E(field: v, …)` fires the event: it calls every @On(E) listener, in
-# declaration order, as a direct call — the whole thing desugars to code, with no
-# runtime and no dispatch table. A program that declares no `event` is compiled
-# byte-for-byte as before (the subsystem is gated on `g_events`).
-#
-# Running it prints:  5 8 20 30 999 42 42
-program Events {
-  event Hurt    { entity: int = 0, amount: int = 0 }   # a payload with fields + defaults
-  event Cleared { }                                    # an empty payload is allowed
-
-  @On(Hurt) handler Flash { print(amount) }            # listeners bind payload fields by name
-  @On(Hurt) handler Guard { print(entity + amount) }   # a second listener, run after the first
-  @On(Cleared) handler Cheer { print(999) }
-
-  entry {
-    emit Hurt(entity: 3, amount: 5)       # -> Flash 5, Guard 3+5=8
-    emit Hurt(entity: 10, amount: 20)     # -> Flash 20, Guard 10+20=30
-    emit Cleared()                        # -> Cheer 999
-    emit Hurt(amount: 42)                 # entity defaults to 0 -> Flash 42, Guard 0+42=42
-  }
-}