fix(provider): prefer per-model temperature over agent override

`ProviderTransform.temperature(model)` encodes per-model-family temperature
values that the model's provider requires (e.g. Moonshot's kimi-k2.* returns
HTTP 400 "invalid temperature: only 1 is allowed for this model" if any
other value is sent). The session/llm.ts call site consulted it in the wrong
order:

  input.agent.temperature ?? ProviderTransform.temperature(input.model)

so the built-in title agent's hard-coded `temperature: 0.5` (agent.ts:271)
won over the kimi-required 1.0, and Moonshot rejected the request.

Swap the operands. The transform value, when present, is the model-aware
answer and should beat a generic agent default. For models that aren't in
the transform map, the function returns `undefined` and the agent's
preference still applies through `??` fallthrough.

Affects: kimi-k2.* (incl. k2.6, thinking, k2-5), gemini, glm-4.6/4.7,
minimax-m2, qwen — anywhere the transform has an entry.

Author: bcode

packages/opencode/src/session/llm.ts

@@ -169,7 +169,7 @@ const live: Layer.Layer<
         },
         {
           temperature: input.model.capabilities.temperature
-            ? (input.agent.temperature ?? ProviderTransform.temperature(input.model))
+            ? (ProviderTransform.temperature(input.model) ?? input.agent.temperature)
             : undefined,
           topP: input.agent.topP ?? ProviderTransform.topP(input.model),
           topK: ProviderTransform.topK(input.model),