Return errors from schema generation instead of panicking

jsonSchemaFor panicked on unsupported types, which meant
FunctionTool, NewOutputType, and RunTyped would crash the
process during setup rather than returning a normal error.

Signed-off-by: Bryan Frimin <bryan@getprobo.com>

pkg/agent/agent_tool.go

@@ -40,7 +40,7 @@ type (
 )
 
 var (
-	agentToolParamsSchema = jsonSchemaFor[agentToolParams]()
+	agentToolParamsSchema = mustJSONSchemaFor[agentToolParams]()
 )
 
 func agentToolDepth(ctx context.Context) int {