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/chronorift/world.ludic

@@ -1,43 +0,0 @@
-# world.ludic — the data model: components, entity archetypes, constants.
-# Imported by examples/chronorift.ludic. No `game` wrapper (this is a fragment).
-
-property Pos    { x: int = 0, y: int = 0 }
-property Actor  { kind: int = 0 }
-property Stats  { hp: int = 1, maxhp: int = 1, mp: int = 0, maxmp: int = 0,
-                   atk: int = 1, def: int = 0, lvl: int = 1, xp: int = 0, guard: int = 0 }
-property Party  { slot: int = 0 }
-
-# Entity KINDS. Identity is stored as one integer per entity (L_kind), not as
-# an empty marker component. Query membership with {Player} / {Enemy}.
-model Player { Pos, Actor, Party, Stats }   # the controllable knight
-model Ally   { Party, Stats }               # backline mage (no overworld body)
-model Enemy  { Actor, Stats }               # battle foe
-
-const MW: int = 40
-const MH: int = 18
-
-const SPR_GRASS: int = 0
-const SPR_TREE:  int = 1
-const SPR_PATH:  int = 2
-const SPR_HOUSE: int = 3
-const SPR_DOOR:  int = 4
-const SPR_HERO:  int = 5
-const SPR_SLIME: int = 6
-const SPR_SKEL:  int = 7
-const SPR_BOSS:  int = 8
-const SPR_MAGE:  int = 9
-const SPR_FLOOR: int = 10
-const SPR_WALL:  int = 11
-
-var game_mode: int = 0    # 0 field, 1 battle, 2 gameover, 3 victory
-var turn_phase: int = 0
-var menu_cursor: int = 0
-var encounter: int = 0
-var enemy_type: int = 0    # 0 slime, 1 skeleton, 2 boss
-var player_hit: int = 0
-var enemy_hit: int = 0
-var gold: int = 0
-var world_map: int = 0    # 0 overworld, 1 dungeon
-var boss_down: int = 0    # boss defeated flag
-var ack: int = 0   # debounce for end screens
-var potions: int = 0  # potions in inventory