release: v0.2.9 (#447)

* feat(llm): add GLM-5.3-Flash, Qwen3.8-Flash, and Tencent HY4 preview

GLM-5.3-Flash on Zhipu, Zhipu Coding Plan and OpenRouter; Qwen3.8-Flash on
DashScope, DashScope Coding Plan and OpenRouter; HY4 preview on OpenRouter.
All three get explicit 1M-class context-window entries so they are not
caught by the glm-5 family fallback (203K) or the 200K default.

* chore: update wechat_group image asset

* chore: update version to v0.2.9

uv.lock moves to deepagents 0.7.11 with its raised dependency floors
(langchain 1.3.18, langchain-core 1.6.1, langchain-anthropic 1.7.0,
langchain-google-genai 4.3.7, langsmith 0.11.2); langgraph stays 1.2.11.

* docs: use umbrella provider names in v0.2.9 changelog

.github/assets/badge-pypi-dark.svg

@@ -5,5 +5,5 @@
   <rect x="54" y="5" width="62" height="24" rx="6" fill="#1565c0"/>
   <text x="85" y="22" text-anchor="middle"
         font-family="Inter, -apple-system, system-ui, sans-serif"
-        font-size="13" font-weight="700" fill="#ffffff">v0.2.8</text>
+        font-size="13" font-weight="700" fill="#ffffff">v0.2.9</text>
 </svg>

.github/assets/badge-pypi-light.svg

@@ -5,5 +5,5 @@
   <rect x="54" y="5" width="62" height="24" rx="6" fill="#2563eb"/>
   <text x="85" y="22" text-anchor="middle"
         font-family="Inter, -apple-system, system-ui, sans-serif"
-        font-size="13" font-weight="700" fill="#ffffff">v0.2.8</text>
+        font-size="13" font-weight="700" fill="#ffffff">v0.2.9</text>
 </svg>