docs: document completion verdict and bump version to 1.3.10

CHANGELOG 1.3.10 (unreleased) with behaviour-change and breaking
sections, README capability rows and a 1.3.10 section, ARCHITECTURE
section 15 plus 6.2/7 updates, schema doc for the stream_end column,
migration impact notes, ROADMAP entry, .env.example MISSING_DONE
semantics, and a revision pointer on the 1.3.9 design. Follow-ups
filed as #32 and #33.

pyproject.toml

@@ -4,7 +4,7 @@ build-backend = "setuptools.build_meta"
 
 [project]
 name = "polygateway"
-version = "1.3.9"
+version = "1.3.10"
 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。