fix: fix multiple bugs in web search, prompts, and tool definitions

[Ricardo-M-L]

Summary

• Fix failed_engines list never being populated in web_search.py — logging about failed/retried engines was dead code
• Fix missing space in SYSTEM_PROMPT string concatenation in manus.py
• Fix print with %s format string in agent_executor.py (should use f-string)
• Fix GoogleSearchEngine returning raw dict instead of SearchItem object
• Fix wrong type annotation str → dict in ask_human.py parameters

Test plan

• Verify web search correctly logs failed engines
• Verify SYSTEM_PROMPT renders with proper spacing
• Verify Google search returns proper SearchItem objects

🤖 Generated with Claude Code

[Ricardo-M-L]

Friendly bump — this fork PR's workflow run is stuck on action_required (GitHub's default for first-time contributors). Could a maintainer approve the workflow so CI can report a verdict? Thanks!