docs: refresh the M3 capability evidence with the 08-25 retest

can_disable stays true — reasoning_effort=none still lands prompt 194,
completion 3, no prose. What the retest added are two limits worth
recording: the verdict is unobservable on the non-streaming path, where
reasoning is billed but neither prose nor usage detail comes back, and
enable_thinking / thinking:{enabled} remain inert on this model.

No behaviour changed, so there is no failing test to show first. The
evidence for a declaration that still holds is the retest itself, not
a unit test the library could write about its own claim.

src/polygateway/thinking.py

@@ -68,7 +68,13 @@ DEFAULT_CAPABILITIES: Mapping[str, ThinkingCapability] = MappingProxyType(
     {
         "MiniMax-M3": ThinkingCapability(
             can_disable=True,
-            evidence="2026-08-02 经 new-api 中转实测 N=10: reasoning_effort=none 稳定关闭,零跳变",
+            evidence=(
+                "2026-08-02 经 new-api 中转实测 N=10: reasoning_effort=none 稳定关闭,零跳变;"
+                "2026-08-25 复测依然成立(prompt 194 = 基线、completion 3、无推理正文)。"
+                "两条限制(findings 2026-08-25-thinking-observability-regression §3.1/§5): "
+                "① 非流式路径观测不到推理信号——推理已计费,但正文与 usage 明细都不回传;"
+                "② enable_thinking / thinking:{type:enabled} 对本模型无效,仅 reasoning_effort 是真开关"
+            ),
         ),
         "MiniMax-M2.7": ThinkingCapability(
             can_disable=False,