Clarify default database location

.env.example

@@ -34,9 +34,17 @@ OPENAI_API_KEY=
 # VECTOR_BACKEND=qdrant
 # QDRANT_URL=http://localhost:6333
 
-# Database/vector paths are auto-detected for macOS, Windows, and Linux.
-# Override only if you intentionally want a custom location.
+# Database path defaults to the operating system app-data folder:
+#   macOS:   ~/Library/Application Support/RA-H/db/rah.sqlite
+#   Linux:   ~/.local/share/RA-H/db/rah.sqlite
+#   Windows: %APPDATA%/RA-H/db/rah.sqlite
+#
+# Set SQLITE_DB_PATH before setup if you intentionally want a repo-local DB,
+# demo DB, or any other separate location.
 # SQLITE_DB_PATH=/absolute/path/to/rah.sqlite
+
+# sqlite-vec extension path is auto-detected for macOS, Windows, and Linux.
+# Override only if you intentionally want a custom extension location.
 # SQLITE_VEC_EXTENSION_PATH=/absolute/path/to/vec0.<dylib|dll|so>
 
 # App config (no changes needed)