Establish independent Fifth domain source root and retire direct brain writers

.gitignore

@@ -0,0 +1,23 @@
+# The Fifth domain keeps its living state outside Git's source history.
+.DS_Store
+**/.DS_Store
+**/__pycache__/
+**/*.pyc
+**/.venv/
+**/venv/
+**/node_modules/
+**/brain-state.json
+**/transition-log.jsonl
+**/WAKE-CONTEXT.json
+**/HEARING-STATE.json
+**/HEARING-LOG.jsonl
+**/memory/
+**/corpus-staging/
+**/store/
+**/cache/
+**/*.sqlite
+**/*.sqlite3
+**/*.key
+**/*.pem
+**/*.p12
+**/*.pfx