feat(curator): vendor the backend application under scenarios/curator/backend

The curator app (Python backend, tests, systemd units, config, scripts) now lives in this repo under scenarios/curator/backend, exported from the standalone checkout's tracked tree (.pi mirror, venv and caches excluded). 149 unit tests pass from the new location; _SHARED_LIB and eval GOLDEN_DIR resolve unchanged. History not preserved per decision.

verify-no-secrets: the ASSIGN heuristic now requires the value to carry entropy (a digit or uppercase letter), so vendored Python kwargs like token=extraction_token no longer false-positive while real base64/hex/random secrets still trip it.

scenarios/curator/backend/pyproject.toml

@@ -0,0 +1,16 @@
+[project]
+name = "curator-media-library"
+version = "0.1.0"
+description = "LAN-first personal book, film, TV and music curation service"
+requires-python = ">=3.12"
+
+[project.scripts]
+curator = "curator.cli:main"
+
+[build-system]
+requires = ["setuptools>=75"]
+build-backend = "setuptools.build_meta"
+
+[tool.setuptools]
+packages = ["curator"]
+