Phase 1: pytest baseline, production hardening, pinned requirements

Establishes the safety net required before any structural refactor.

Tests (tests/):
- conftest.py rewritten for Flask-SQLAlchemy 3.x (drop-recreate per
  test, StaticPool-shared in-memory SQLite, admin_user + auth_headers
  fixtures). Removes deprecated db.create_scoped_session pattern.
- test_smoke.py: 8 baseline tests (app boot, JWT login valid+invalid,
  protected routes, paginated response shape, plugin auto-discovery).
- test_security_config.py: 7 tests pinning ProductionConfig.validate
  failure modes (missing/dev SECRET_KEY, missing JWT_SECRET_KEY,
  missing DATABASE_URL, wildcard CORS, empty CORS) and one happy-path.

Production hardening (shopdb/config.py, shopdb/__init__.py):
- ProductionConfig.validate() raises ConfigError on missing or
  insecure SECRET_KEY, JWT_SECRET_KEY, DATABASE_URL, CORS_ORIGINS.
  No silent fallback to dev defaults in production.
- create_app invokes validate() when config_name == 'production'.
- CORS_ORIGINS default no longer wildcard; defaults to localhost
  Vite dev origin.
- Drop os.path.exists probe in serve_frontend (path-traversal risk
  surface). send_from_directory handles safe-join + 404 itself.
- Replace User.query.get with db.session.get (SQLAlchemy 2.0 API).

TestingConfig (shopdb/config.py):
- Add StaticPool + check_same_thread connect_args so SQLite in-memory
  is shared across the test session.

Index dedup (plugins/printers/models/printer_extension.py):
- Rename idx_printer_windowsname -> idx_printerdata_windowsname.
  Two model classes (Printer, PrinterData) declared the same index
  name; SQLite enforces global index uniqueness even across tables.
  Per CONTRIBUTING.md naming convention, indexes follow
  idx_<table>_<column>.

Dependency pinning (requirements.in, requirements.txt):
- requirements.in holds the loose source pins (the human-edited file).
- requirements.txt is now a uv-compiled lockfile (every transitive
  dep pinned to an exact version). Reproducible builds. Run
  `uv pip compile requirements.in -o requirements.txt` to refresh.

Test count: 0 -> 15 passing. All naming/style checks still green.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

requirements.in

@@ -0,0 +1,32 @@
+# Flask and extensions
+flask>=3.0
+flask-sqlalchemy>=3.1
+flask-migrate>=4.0
+flask-jwt-extended>=4.6
+flask-cors>=4.0
+flask-caching>=2.0
+flask-marshmallow>=1.2
+marshmallow-sqlalchemy>=0.29
+
+# Database
+mysql-connector-python>=8.0
+pymysql>=1.1
+
+# CLI and utilities
+click>=8.1
+python-dotenv>=1.0
+tabulate>=0.9
+
+# HTTP/API clients
+requests>=2.31
+
+# Security
+werkzeug>=3.0
+
+# Validation
+email-validator>=2.0
+
+# Testing
+pytest>=7.0
+pytest-flask>=1.2
+pytest-cov>=4.0