fix: add .dockerignore and env_file to docker-compose

Prevents .env from being baked into Docker image (was overriding
config defaults). Adds env_file directive so containers load host
.env properly.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

.dockerignore

@@ -0,0 +1,21 @@
+.env
+.env.*
+!.env.example
+.git
+.gitea
+.gitlab-ci.yml
+__pycache__
+*.pyc
+*.pyo
+site/
+docs/
+exports/
+alembic/versions_backup/
+*.csv
+*.md
+!requirements.txt
+.pre-commit-config.yaml
+.architecture-rules/
+.performance-rules/
+.security-rules/
+mkdocs.yml