Replace Make with just

[khaykingleb]

Replace the Makefile with a grouped, discoverable justfile modeled on khaykingleb/investment-workbench after the infrastructure and uv migrations settle the repository's command surface.

Depends on #12 and #13.

Scope

• Replace all remaining development, quality, experiment, and container Make recipes with just recipes.
• Use grouped recipes and concise documentation similar to the finance repository.
• Update CI and documentation references.
• Remove the Makefile completely.

Acceptance criteria

• just is pinned in .tool-versions.
• Running just lists grouped, documented commands.
• Recipes cover setup/sync, hooks, tests, aggregate quality checks, local experiment execution, image build, and container shell/run workflows.
• Recipes use frozen uv environments where reproducibility matters.
• just check runs the complete local quality gate.
• The Makefile is deleted.
• CI and documentation contain no Make references.

Out of scope

• Infrastructure recipes removed by Extract infrastructure into a standalone K3s example repository #12
• Kubernetes experiment submission recipes
• Redesigning the experiment CLI