refactoring(cli/mcp): refactoring error msg

[VascoSch92]

Replaced 6 identical try/except MCPConfigurationError blocks with a single @_mcp_error_handler decorator, and
extracted the repeated "restart session" message into _print_restart_hint().

Why: Duplicated error handling is a maintenance risk — if the error format, exit code, or styling ever needs to change,
you'd have to update 6 places instead of 1. The decorator makes each handler purely about its happy-path logic, which is easier to read and less prone to inconsistencies.

---

🚀 Try this PR

uvx --python 3.12 git+https://github.com/OpenHands/OpenHands-CLI.git@vasco/refactoring-mcp

[github-actions]

Coverage Report •

File	Stmts	Miss	Cover	Missing
openhands_cli/mcp
mcp_commands.py	103	1	99%	160
TOTAL	6634	930	85%

[all-hands-bot]

🟢 Good taste - This is textbook refactoring done right.

Verdict: ✅ Worth merging

Analysis:
Clean DRY refactoring that eliminates 6 identical try/except blocks and 3 identical restart hints. The decorator is simple (no complex nesting), preserves behavior exactly, and makes the code more maintainable. Each handler is now pure happy-path logic, which is easier to read and modify.

Key Insight: This is what refactoring should be - removing duplication with a standard pattern without adding complexity or changing behavior.

No critical issues found. If this module has tests, verify they still pass (though they should, since behavior is preserved).