NewLogic now takes (FileSystem, path, openfunc); update the e2e harness
and editor tests accordingly. The harness uses a no-op openfunc, matching
impl_other.go (the real app's OpenFile is a platform bridge, no-op off
Android).
Also adds doc/development_plan.md (draft, with corrections note re: the
live repo state).
- Add detailed §15 lazy loading plan with 7 implementation steps
- Update Phase 2 checklist with specific tasks
- Add E2E test harness for browser files
- Refactor browser layout and handler structure
- Add .gitignore for common patterns
WIP: Actual lazy loading not yet implemented.