chore(re): stop committing game assets; captures stay local

Issue #49: the repos carry code, tooling and docs only.

Untracks 143 screenshots, 3 savegame blobs and `tools/re-capture/ob_digits.png`
(a digit-template sheet cut from game frames) -- 146 files, 76.4 MB. They stay
in the working tree and are gitignored, so the pages' relative links still
resolve where the captures exist and nothing ships.

Derived measurements (csv/tsv/txt/log/json/jsonl/npy) are our own numbers, not
game content, and stay tracked -- they are what most claims rest on.

`check-capture-citations` had its contract inverted, and it is the half worth
reading:

  * presence now comes from the WORKING TREE, not `git ls-files`. The assets are
    deliberately untracked, so asking the index would report every screenshot as
    missing and fail all 203 citations.
  * a NEW failure: a game asset that IS tracked. A screenshot that sneaks back
    in is invisible in review -- a binary shows as "Bin 0 -> 1234567 bytes" --
    and is permanent once merged, since removing it later needs a history
    rewrite. So that half has to be loud.

Verified:
  * selftest 8/8, including the new rule
  * scan: 212 present, 212 cited, 0 dangling, 0 tracked  -> exit 0
  * force-add one PNG -> "game assets TRACKED: 1", exit 1, selftest red

⚠️ This does NOT remove the blobs from history; a clone still fetches them.
That needs a filter-repo rewrite and a force-push, which is a separate,
human-run step.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

docs/re/README.md

@@ -18,6 +18,22 @@ A wrong-but-confident note is worse than no note: someone builds on it and the b
 for weeks. Every entry therefore carries an explicit **confidence** and its **evidence**.
 This mirrors the project method — *measure the oracle, never infer; refute before believing.*
 
+### Captures are local-only (issue #49)
+
+The repository carries **code, tooling and docs**. Screenshots and savegame
+blobs are game-derived, so since 2026-09-19 they live in `docs/re/captures/`
+on disk and are **gitignored** — the pages' relative links still resolve on a
+machine that has them, and nothing ships.
+
+Derived measurements (`csv`, `tsv`, `txt`, `log`, `json`, `jsonl`, `npy`) are
+our own numbers rather than game content, and stay tracked — they are what most
+claims here actually rest on.
+
+`tools/re/check-capture-citations` enforces both halves: a cited capture must be
+**present**, and a game asset must **not be tracked**. ⚠️ A fresh clone has no
+captures, so its citations will not resolve until the captures are copied in;
+that is expected, and the checker is a local gate rather than a CI one.
+
 ### Clean-room firewall
 
 - ✅ Allowed: behaviour descriptions, field offsets/types, formulas, state machines,

docs/re/captures/.gitignore

@@ -0,0 +1,13 @@
+# Game-derived assets stay on disk and ship nowhere (issue #49).
+#
+# The pages' relative links still resolve on a machine that has the captures,
+# so the evidence stays followable where it exists — it is simply not committed.
+# `tools/re/check-capture-citations` enforces both halves: a cited capture must
+# be PRESENT here, and an asset must NOT be tracked.
+#
+# Derived measurements (csv, tsv, txt, log, json, jsonl, npy) are our own
+# numbers rather than game content, and remain tracked.
+*.png
+*.jpg
+*.jpeg
+*.bin