docs: REUSE.md introduced — cross-repo reuse map (exec/format-safety guards, durable-id seams, traps; docs-only, no version bump)

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01PSK5g6qYLknKj8u3QAFEr6

CONTEXT.md

@@ -5,6 +5,7 @@
 
 ## Current
 
+- **2026-07-03 — `REUSE.md` exists at the repo root** (canonical helpers / format-safety guards / traps / seams, code-verified); maintenance rule active: update it in the same commit that changes a shared helper.
 - **v0.61.0** (2026-07-03) — blast-radius audit fixes **B1 + D1 + D2 + D3** from
   `felhom.eu/documentation/audits/AUDIT-blast-radius-hostroot-localapi-2026-07-02.md`: random temp
   staging for root-installed scripts (+ sudoers/manifest glob updates), mkfs-wrapper member/RO