docs: record thinking-switch findings and capability design (issue #5, #6)

Findings: live-API measurements across MiniMax M3/M2.7/M2.5, qwen and
deepseek, plus a survey of how nine unified gateways model per-model
parameter divergence. Key facts: reasoning_effort is MiniMax's real
switch, M2.x reasoning is mandatory and cannot be disabled, and the
relay's local token-count fallback silently drops reasoning_tokens.

Design: keep the parameter shape at provider level, push capability
down to model level, split "unknown" / "unsupported" / "no opinion"
into three distinct values, and fail at assembly time when a model
cannot honour enable_thinking=False.

research-wiki/graph/edges.json

@@ -223,6 +223,13 @@
       "relation": "implements",
       "evidence": "11 个任务逐条覆盖设计的决策 A-G 与 §5 的 14 条测试清单",
       "added": "2026-07-31T16:59:35.657367+00:00"
+    },
+    {
+      "source": "finding:2026-08-02-thinking-switch-and-reasoning-tokens",
+      "target": "design:2026-08-02-thinking-capability-design",
+      "relation": "supports",
+      "evidence": "供应商实测与业界调研为该设计的形态/能力分层与失败语义提供事实依据",
+      "added": "2026-08-02T09:38:57.033054+00:00"
     }
   ]
 }