fix(test): prevent config file from leaking kagi token into search test

The search token validation test only cleared KAGI_TOKEN from the
environment but still loaded the user config file, which could supply
the token and cause the test to pass incorrectly. Pass
--config=/nonexistent/path so loadConfig returns an empty object.

Also includes search command improvements: markdown/json format output
and --format flag.

test/smoke.js

@@ -163,7 +163,7 @@ test(
 test("search validates kagi token in provider", ["search", "errors"], () => {
   const env = { ...process.env };
   delete env.KAGI_TOKEN;
-  const result = runCli(["search", "example query"], { env });
+  const result = runCli(["search", "--config=/nonexistent/path", "example query"], { env });
   const output = parseJson(result.stderr);
 
   assert.notEqual(result.status, 0, result.stdout || result.stderr);