chore: prepare release 1.3.5

Version bump in pyproject and __init__, CHANGELOG dated 2026-09-09,
README install lower bound raised to >=1.3.5, and release-prep evidence
(remote check, gates, real gateway smoke and one bounded live probe)
recorded in the 1.3.5 validation finding.

pyproject.toml

@@ -4,7 +4,7 @@ build-backend = "setuptools.build_meta"
 
 [project]
 name = "polygateway"
-version = "1.3.4"
+version = "1.3.5"
 description = "PolyGateway：实验室统一的大语言模型（LLM/VLM/OCR）调度与中转库——多源、限流、重试、熔断、缓存、遥测"
 # registry 包页面的正文只认这一项:缺了页面就是一片空白(1.1.2 的教训,twine 会警告
 # long_description missing 但不阻塞上传)。README 在打包时被固化进产物,发布后再改无效。