Remove unnecessary documentation

Removed 16 files that were agent work, implementation tracking, or aspirational planning:

- docs/BUILD_OUTPUT_CLEANUP.md - build optimization tracking
- docs/STYLESHEET-DOCUMENTATION-UPDATE.md - agent work summary
- docs/spc-refactor-roadmap.md - implementation tracking
- docs/product-marketing-onboarding.md - marketing planning
- docs/guides/macro-parity-tracking.md - internal tracking
- docs/data-visualisation/DATA-VIZ-BURNDOWN.md - sprint tracking
- docs/data-visualisation/ENHANCED-RENDERERS-SUMMARY.md - agent summary
- docs/roadmaps/DATA-VIZ-BURNDOWN.md - sprint tracking
- docs/roadmaps/SPC_V2_SQL_PARITY_BURNDOWN.mdx - implementation tracking
- docs/roadmaps/DOCUMENTATION-UPDATES-SUMMARY.md - agent summary
- docs/roadmaps/ENHANCED-RENDERERS-SUMMARY.md - agent summary
- docs/roadmaps/clinical-operations-extensions.md - future planning
- docs/roadmaps/govuk-parity-gap-analysis.md - gap analysis
- docs/roadmaps/ukhsa-data-viz-parity-gap-analysis.md - gap analysis
- docs/roadmaps/lms-extensions.md - future extensions
- docs/roadmaps/ai-interaction-roadmap.tsx - AI planning doc

Retained all developer reference documentation useful for new contributors.

Author: fergusbisset