Improve container

[thorinaboenke]

Task

#220

Description

• Add .dockerignore
• Pin previously-floating :latest images to versions
• Add docker/docker-compose entries to dependabot.yml so pins get bumped automatically
• Switch Dockerfile/Dockerfile-dev from uv pip install to uv sync Using uv lock
• Split the sync into a deps-only layer (--no-install-project) followed by the project-install layer, so editing source no longer invalidates the dependency-install cache.

also fix bind-mount paths depending on calling directory
docker-compose.yml and docker-compose.tls.yml built bind-mount host paths as $PWD/container/.... $PWD is the shell's current directory, nothing to do with where the compose file lives. Running docker compose up from
any directory other than the repo root (e.g. from container/) silently mounted the wrong, non-existent paths (container/container/...)
Replaced $PWD/container/... with ./container/.... Composeresolves relative paths in volumes: against the compose file's own directory

• Add docker-compose.override.yml to .gitignore and ship docker-compose.override.yml.example as a template

• multistage build for fluentd container

How Has This Been Tested?

docker build on both Dockerfile and Dockerfile-dev, verified detectmate --help and entry points resolve correctly
Confirmed dependency layer stays CACHED on a source-only rebuild
docker compose config validates after image pin changes

fluentd dry-run works in new image

also ran docker compose with the new fluent image.

Checklist

• This Pull-Request goes to the development branch.
• I have successfully run prek locally.
• I have added tests to cover my changes.
• I have linked the issue-id to the task-description.
• I have performed a self-review of my own code.