fix: add missing tools to hello-world and test-engineer templates

- hello-world: add file_write (LLM needs it for writing files)
- test-engineer: add web_fetch, web_search (needed for researching test patterns)

agents/hello-world/agent.toml

@@ -34,6 +34,7 @@ max_llm_tokens_per_hour = 100000
 [capabilities]
 tools = [
   "file_read",
+  "file_write",
   "file_list",
   "web_fetch",
   "web_search",