fix(adapters): drop dead search_filter parameter from to_mcp handle_batch (PRJ-24)

The batch tool's input schema declares no query field, so the parsed
search_filter was computed then discarded with 'let _ ='. Remove the
parameter and the discard; call sites pass only (arguments, identity).

src/adapters/to_mcp.rs

@@ -208,7 +208,6 @@ impl ToMcpGateway {
 
     async fn handle_batch(
         &self,
-        search_filter: Option<String>,
         arguments: Option<JsonObject>,
         identity: Option<Identity>,
     ) -> CallToolResult {
@@ -242,7 +241,6 @@ impl ToMcpGateway {
                 .await;
             results.push(envelope_to_value(response));
         }
-        let _ = search_filter;
         CallToolResult::structured(serde_json::json!({ "results": results }))
     }
 }
@@ -458,7 +456,7 @@ impl rmcp::handler::server::ServerHandler for ToMcpGateway {
                 TOOL_SEARCH => this.handle_search(search_filter, identity).await,
                 TOOL_SCHEMA => this.handle_schema(arguments, identity).await,
                 TOOL_CALL => this.handle_call(arguments, identity).await,
-                TOOL_BATCH => this.handle_batch(search_filter, arguments, identity).await,
+                TOOL_BATCH => this.handle_batch(arguments, identity).await,
                 unknown => {
                     let err = CallError::new(
                         "NOT_FOUND",
@@ -710,11 +708,7 @@ mod tests {
             TOOL_SEARCH => gateway.handle_search(search_filter, identity).await,
             TOOL_SCHEMA => gateway.handle_schema(arguments, identity).await,
             TOOL_CALL => gateway.handle_call(arguments, identity).await,
-            TOOL_BATCH => {
-                gateway
-                    .handle_batch(search_filter, arguments, identity)
-                    .await
-            }
+            TOOL_BATCH => gateway.handle_batch(arguments, identity).await,
             unknown => {
                 let err = CallError::new(
                     "NOT_FOUND",