Architecture: identify hardcoded assumptions and create a removal plan

[dlrice]

Goal

• Make hardcoded assumptions explicit and plan how to remove them safely.

Scope

• List major hardcoded assumptions (data sources, track definitions, rendering constraints, etc.)
• Categorise as: must-remove (grant scope), nice-to-have, or keep-for-compatibility
• Propose approach for making these configurable (high-level)

Acceptance criteria

• Written list + categorisation
• Follow-on issues created for each must-remove item