Add local-network deployment automation and tighten runtime defaults

This commit adds the first complete local-network deployment path for the project. It normalizes the runtime contract around a fixed container listener on 0.0.0.0:10000, binds the published compose port to 127.0.0.1, and keeps the image/build workflow aligned with the released container image.

It also introduces an installation script, an nginx reverse-proxy template, and a safer SQLite backup flow based on sqlite3 .backup with retention and optional rclone upload support. Deployment-oriented configuration has been consolidated into .env.example, repository-local .env files are now ignored, and the deployment scripts are executable.

In addition, the frontend mixed-content issue is fixed by switching the stylesheet reference to a root-relative static path, with tests updated to cover the regression. README guidance has been expanded to document the new install, nginx, backup, and restore conventions.

.gitignore

@@ -2,6 +2,7 @@
 __pycache__/
 .pytest_cache/
 *.pyc
+.env
 data/*.db
 
 # macOS generated files