fix: prioritize CLI --model argument over command markdown model

Fixes #17783

The CLI --model argument should have highest priority according to docs,
but it was being overridden by model specified in command/agent markdown.

Changed the priority order in session/prompt.ts to check input.model
(CLI argument) before falling back to command.model and command.agent model.

Author: Nainish-Rai

packages/opencode/src/session/prompt.ts

@@ -1804,6 +1804,7 @@ NOTE: At any point in time through this workflow you should feel free to ask the
     template = template.trim()
 
     const taskModel = await (async () => {
+      if (input.model) return Provider.parseModel(input.model)
       if (command.model) {
         return Provider.parseModel(command.model)
       }
@@ -1813,7 +1814,6 @@ NOTE: At any point in time through this workflow you should feel free to ask the
           return cmdAgent.model
         }
       }
-      if (input.model) return Provider.parseModel(input.model)
       return await lastModel(input.sessionID)
     })()