refactor(agents): migrate .agent/ planning tree to .agents/

Standardize on the .agents/ directory (shared with project skills):
phases/, user_stories/, reports/, screenshots/, validate.sh, and
phase-sessions/ + pipeline.log all move to .agents/ (git mv preserves
history; runtime artifacts move alongside).

Updates every reference in AGENTS.md, README.md, .gitignore, app
docstrings, and test story headers. Historical KB content in data/
and the runtime pipeline.log transcript are left untouched.

.agents/reports/02_story_import_documents.a3.validate

@@ -0,0 +1,21 @@
+ImportError while loading conftest '/var/home/ducoterra/Projects/Personal/brain_of_reese/tests/conftest.py'.
+tests/conftest.py:7: in <module>
+    from app.main import app as fastapi_app
+app/main.py:17: in <module>
+    from app.api.health import router as health_router
+app/api/health.py:7: in <module>
+    from app.db import db_available
+app/db.py:21: in <module>
+    engine = create_engine(get_settings().database_url, pool_pre_ping=True, future=True)
+             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+../../../.local/lib/python3.14/site-packages/sqlalchemy/util/deprecations.py:281: in warned
+    return fn(*args, **kwargs)  # type: ignore[no-any-return]
+           ^^^^^^^^^^^^^^^^^^^
+../../../.local/lib/python3.14/site-packages/sqlalchemy/engine/create.py:617: in create_engine
+    dbapi = dbapi_meth(**dbapi_args)
+            ^^^^^^^^^^^^^^^^^^^^^^^^
+../../../.local/lib/python3.14/site-packages/sqlalchemy/dialects/postgresql/psycopg.py:495: in import_dbapi
+    import psycopg
+E   ModuleNotFoundError: No module named 'psycopg'
+All checks passed!
+validation FAILED (see output above)