refactor: complete migration to template-v2 architecture

- Remove legacy template.svg files from example/ and my-project/
- Simplify generator.js by removing generateHardcoded method (326→210 lines, -36%)
- Add strict template validation with clear error messages
- Remove all fallback mechanisms - template-v2.svg format now required
- Clean up tests: remove hardcoded generation tests, keep template-based tests
- Add comprehensive e2e tests (large datasets, edge cases, error handling)
- Update documentation: mark REFACTORING_PLAN.md complete, add TEMPLATE_V2_GUIDE.md
- All 56 tests passing (16 engine + 25 generator + 15 integration)

BREAKING CHANGE: Old template.svg format no longer supported. Must use template-v2.svg with <g id="*-template"> elements in defs section.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

example/project.json

@@ -3,7 +3,7 @@
   "description": "Neutrales Beispielprojekt f\u00fcr die Timeline Engine.",
   "dataSource": "sample.csv",
   "stylesheet": "style.css",
-  "svgTemplate": "template.svg",
+  "svgTemplate": "template-v2.svg",
   "settings": {
     "timelineMonths": 18
   },