chore: repo scaffolding via /repo-init

Add .gitignore (Python stack + obligatory lines; /STATE.md kept local-only
until a private remote exists), CHANGELOG.md, and the Communication patterns
section in CLAUDE.md. STATE.md is gitignored — must never reach the public
open/ mirror.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01K8GmKRCdsPjWYAKWsNgeQS

.gitignore

@@ -0,0 +1,25 @@
+# --- STATE.md: LOCAL-ONLY until a PRIVATE remote exists ---
+# House rule: STATE.md must never reach a public mirror. No private remote is set
+# yet (see docs/BRIEF.md §13.4) and this repo is intended for publication, so the
+# current state-of-play stays untracked. Move STATE.md to tracked ONLY after a
+# private Forgejo remote is added — never on a public mirror.
+/STATE.md
+
+# --- Python (declared stack: stdlib-first library, BRIEF §8) ---
+__pycache__/
+*.pyc
+.venv/
+build/
+dist/
+*.egg-info/
+.pytest_cache/
+.mypy_cache/
+.ruff_cache/
+.coverage
+coverage/
+
+# --- Secrets / local / OS (obligatory) ---
+.env
+.env.*
+*.local.md
+.DS_Store