security: disposition the one historical gitleaks finding (infra#326)

A Gitea PAT was pasted into a CD-watching curl command in a 2026-04-22
planning doc (c9310b10, last_eight 3105a670).

Verified dead before dispositioning it, rather than assuming: authenticating
GET /api/v1/user with that exact value returns 401. It was almost certainly
invalidated by the early-August rotation of the `mathias` PATs -- the same
rotation whose fan-out caused infra#260, where CI's stale copies kept
failing. So it was killed for unrelated reasons, by luck rather than by the
leak being noticed.

No rotation outstanding. `task security:gitleaks:history` now exits 0 here.

Used .gitleaksignore (per-finding fingerprint) rather than a path allowlist
in .gitleaks.toml: a path allowlist would also blind the working-tree scan
that gates commits. Verified both directions -- history 1 -> 0, working tree
still clean.

.gitleaksignore

@@ -0,0 +1,33 @@
+# Historical gitleaks findings, dispositioned (infra#326 / infra#317).
+#
+# WHY THIS FILE AND NOT .gitleaks.toml:
+# This is a finding in git HISTORY, surfaced by the full-history audit
+# (`task security:gitleaks:history`). The working-tree scan that gates commits
+# (`task security:gitleaks`, the pre-commit hook, CI) is clean. Suppressing by
+# PATH in .gitleaks.toml would also blind the working-tree scan for that file
+# forever; a fingerprint pins one finding in one commit, so a NEW secret in the
+# same file still fires.
+#
+# History is not rewritten here, so the remediation for a real leak is
+# ROTATION -- making the committed value worthless -- never scrubbing.
+#
+# Dispositioned 2026-08-29. Re-check with: task security:gitleaks:history
+
+# --- Real credential, ALREADY DEAD -------------------------------------------
+# A Gitea PAT pasted into a CD-watching command in a planning doc
+# (`Authorization: token <40-hex>`, last_eight 3105a670).
+#
+# Verified dead 2026-08-29: authenticating against
+# GET https://git.d-ma.be/api/v1/user with this exact value returns 401, so the
+# committed token no longer grants anything. It was almost certainly invalidated
+# by the early-August rotation of the `mathias` PATs (the same rotation whose
+# fan-out caused infra#260, where CI copies of the old value kept failing).
+#
+# No rotation action outstanding. Kept as a fingerprint rather than removed from
+# history because history cannot be rewritten here.
+#
+# The generalisable lesson is recorded separately: a credential printed into a
+# doc/transcript is permanent, so the only remedy is rotating it -- which in
+# this case had already happened for unrelated reasons, by luck rather than by
+# the leak being noticed.
+c9310b1079478bf4430b0a2dfb25445d7ccc9b59:docs/superpowers/plans/2026-04-22-phase4-attempt-wiring.md:curl-auth-header:1053