docs: add planning documentation to notes/

Move RN 0.84 upgrade planning documents to notes/ directory:
- MVP_SUPPORT_PLAN.md: Release planning and testing phases
- MVP_TASKS.md: Implementation task checklist
- RN_UPGRADE_BREAKING_CHANGES.md: Breaking changes documentation
- VERSION_SUPPORT_STRATEGY.md: Version support matrix

These are internal planning docs that were originally in the repo root.
Updated .gitignore to allow notes/ for planning documentation.

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

Author: abueide

.gitignore

@@ -101,4 +101,4 @@ AGENTS.md
 *.local.sh
 
 # Notes and research (not for commit)
-notes/
+# notes/ - removed to allow planning docs