docs: add react-router-dom extraction and integration plan (#215)

[15414tdh]

Summary

Created a detailed extraction and migration plan for integrating react-router-dom functionality from PR #194, as requested in issue #215.

Deliverables

• Created docs/ROUTER_INTEGRATION.md documenting:
  • Background on why extraction is needed (PR Add react router #194 is entangled with other changes)
  • Four concrete integration points: Router setup, Route definitions, Navigation, History
  • Code examples showing the before/after for each integration point
  • Four-phase migration strategy to keep each step small and reviewable
  • Mapping of all current wallet pages to their corresponding React Router routes

Why Documentation First

The issue notes that PR #194 bundles router changes with TransactionStore and config.js. Before extracting code, having a clear plan helps:

1. The maintainer can verify the approach before code changes
2. Each phase produces a small, focused PR
3. Future contributors understand the routing architecture

Closes #215

/claim