fix(release): keep generated template changes current

[JSONbored]

Summary

• Fixes the release-prep/template generation mismatch that broke validate-template.py --all after the 1.14.0-aio.1 release PR merged
• Makes the Dify XML generator render the same changelog-derived <Changes> block as the release-prep updater

What changed

• Added shared template change-note helpers for changelog parsing and XML encoding
• Updated generate_dify_template.py and update-template-changes.py to use the same <Changes> rendering logic
• Added a regression test proving the generator uses the latest released changelog section
• Added the shared helper to CI py_compile coverage
• Formatted the generated release changelog so Trunk is clean

Why

• The release workflow updated dify-aio.xml from CHANGELOG.md, but the generator still emitted the original pre-release <Changes> block
• CI calls scripts/validate-template.py --all, which includes the generator freshness check, so main failed immediately after the release PR merge

Validation

• .venv/bin/python scripts/generate_dify_template.py --check
• .venv/bin/python scripts/validate-template.py --all
• bash scripts/validate-derived-repo.sh .
• .venv/bin/python -m pytest tests/unit tests/template
• trunk check --show-existing --all
• git diff --check

Notes

• Do not run publish release against the current failed af11630 release merge commit
• After this fix lands and main is green, rerun Prepare Release so it creates a fresh validated 1.14.0-aio.1 release PR, then merge that PR and run Publish Release