ERB-to-React/SquareKit Migration

Systematic process for converting Rails ERB views to React/SquareKit, learned from the groups/edit.html.erb migration (PRs #17422, #17597, #17603, #17657).

Phase 0: Deep ERB Reconnaissance

This is the most critical phase. Mistakes here cascade through everything.

Before writing any code, build a complete map of the ERB page:

Step 1: Trace the Full Partial Tree

Task Progress:
- [ ] Read the main ERB template
- [ ] List ALL files in the view directory (app/views/<resource>/)
- [ ] Read every partial referenced from the main template
- [ ] Read every partial referenced from those partials (go 3 levels deep)
- [ ] Document the complete partial dependency tree