fix: handle MissingStyle in display_user_input (issue #2962)

[chrislazar25]

Summary: Fix crash when display_user_input() receives a color style Rich can't resolve by catching MissingStyle and falling back to uncolored output.

Technical Details:

• Root Cause: confirm_ask() → user_input() → display_user_input() → self.console.print(Text(inp), **style) raises MissingStyle when user_input_color contains a string not in Rich's style registry (e.g., invalid hex, unregistered theme token). No error handling exists at this call site.
• Mechanism: The user's input is processed, the chat history logged, then display_user_input() attempts to print with the style — and crashes before the message reaches the user. The fix wraps the console.print() call in try/except MissingStyle, falling back to a plain uncolored print.

Verification: Confirmed adherence to CONTRIBUTING.md. Ran python -m pytest tests/ -x -q. 455 passed, 1 failed (test_voice_init_invalid_format — pre-existing, requires audio hardware, reproduces on main). Pre-commit hooks (isort, black, flake8, codespell) all green.

Blast Radius:

• Impact: Low. Only affects the display_user_input code path in io.py.
• Trade-offs: Degraded UX (no color) on style resolution failure versus a hard crash. No behavioral change for valid styles. No performance impact.

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Fixes #2962

[chrislazar25]

Fixes #2962