chore(root): allowlist ARCHITECTURE.adoc and GEMINI.md (#54)

Final root-shape drift on this repository: `ARCHITECTURE.adoc and
GEMINI.md`.

**Owner ruling (2026-09-18):** these stay at the repository root, so the
allowlist names them. Additions only — no file moves, no entry removed.

`scripts/check-root-shape.sh` is a required step in `estate-rules.yml`;
this takes the repository from failing to **green**.

Verified by running this repository's own checker before and after the
change.

Author: hyperpolymath

.machine_readable/root-allow.txt

@@ -47,6 +47,8 @@ sonar-project.properties   # SonarCloud analysis config; the SonarQube scan acti
 .devcontainer/             # VS Code dev container spec; tool-required at root
 .git/
 .github/                   # CONTRIBUTING.md, CODE_OF_CONDUCT.md, SECURITY.md, workflows/
+GEMINI.md                   # agent-tool pointer; read from the repository root by convention (owner ruling, 2026-09-18)
+ARCHITECTURE.adoc           # design overview; stays at root (owner ruling, 2026-09-18)
 www/                       # site-operations bundle; canonical .well-known/ lives at www/.well-known/ (issue #53)
 .machine_readable/         # AI manifests, contractiles, custom-format configs
 .well-known/