Update state.json and development plan to reflect actual progress (~15%)

- state.json: Phase 5 status changed to pending, next steps updated
- DEVELOPMENT_PLAN.md v1.1: Added actual progress, verified current state,
  renumbered phases 5-9, marked all remaining work as PENDING
- Deleted outdated plans (BACKEND_TEST_PLAN, DATA_LOADING_VERIFICATION,
  DOCKER_MIGRATION_PLAN, ENDPOINT_AUDIT, ROADMAP, SIMPLIFICATION_PLAN,
  STATEMENT_OF_INTENT, backend/TEST_PLAN)
- Added new files: DEVELOPMENT_PLAN.md, backend/ARCHITECTURAL_REPORT.md,
  backend/SIMPLIFICATION_SUMMARY.md, backend/run.py, backend/.dockerignore

backend/.dockerignore

@@ -0,0 +1,50 @@
+__pycache__
+*.pyc
+*.pyo
+*.pyd
+.Python
+*.so
+*.egg
+*.egg-info
+dist/
+build/
+.eggs/
+
+.git
+.gitignore
+.gitattributes
+
+.venv/
+venv/
+env/
+
+state.json
+state.yaml
+state.yml
+
+__backup__
+*.bak
+*.old
+
+.env
+.env.*
+!.env.example
+
+.DS_Store
+Thumbs.db
+
+node_modules/
+
+.pytest_cache/
+.ruff_cache/
+htmlcov/
+.coverage
+coverage.xml
+
+*.log
+logs/
+
+.idea/
+.vscode/
+*.swp
+*.swo