docs: add Apache APISIX 3.19.0 release notes

[kayx23]

Summary

• add the English Apache APISIX 3.19.0 release notes for September 28, 2026
• add the corresponding Chinese translation
• validate all 48 entries from chore: release 3.19.0 apisix#13976 against the landed code and intended release tree
• document 11 compatibility-sensitive changes with scoped upgrade plans
• reconcile the final ws/wss behavior introduced by fix(websocket): address review findings on the ws/wss proxy path apisix#13977

Validation

• repository pre-commit Remark checks
• Markdownlint 0.25.0
• JSON, YAML, and shell example parsing
• frontmatter and English/Chinese structure checks
• direct coverage of all 48 changelog PRs in both languages
• whitespace checks

Follow-up

• The source changelog PR remains open; these notes are synchronized through commit 47304362.
• Vale was not run because this repository does not contain a .vale.ini configuration.

Source changelog: apache/apisix#13976