fix: fail malformed model actions

[binichallein]

Summary

• Fixes 工程bug #316 by treating unparseable model actions as explicit failures instead of wrapping them as successful finish(...) actions.
• Prevents malformed outputs such as [{"Type": "Type"}] / [{ 'Type': 'Type' }] from being executed or reported as completed tasks.
• Applies the same failure path to Android/HarmonyOS and iOS agents.

Test Plan

• python -m pytest
• pre-commit run --files phone_agent/agent.py phone_agent/agent_ios.py tests/test_agent_parse_errors.py