feat: quick wins - dockerignore, env secrets, gzip, cache-control

- Add .dockerignore to exclude .git, __pycache__, docs, etc. from Docker context
- Create .env.example template with documented env vars
- Move OBSIGATE_ADMIN_PASSWORD from docker-compose.yml to env_file: .env
- Add .env.* to .gitignore (excluding .env.example)
- Enable GZipMiddleware for ~70% bandwidth reduction on text responses
- Add Cache-Control: immutable for /static/ assets
- Update ROADMAP: mark all 4 quick wins as done, add audit findings
- Add comprehensive technical audit report (AUDIT_TECHNIQUE_2026-05-27.md)

.dockerignore

@@ -1,12 +1,20 @@
-__pycache__/
+.git
+.gitignore
+.gitattributes
+__pycache__
 *.pyc
 *.pyo
-.env
-test_vault/
-.venv/
-venv/
-.git/
-.gitignore
-README.md
-build.sh
+.venv
+venv
+test_vault
+docs
+*.md
+!README.md
 docker-compose.yml
+.env
+.env.*
+*.log
+.obsigate-backup
+.pytest_cache
+htmlcov
+.coverage