fix: Enforce ACP bridge only - remove print mode fallback

Remove all fallback paths that attempted to use a non-functional print mode.
The system now strictly requires the ACP bridge and fails fast if unavailable.

Changes:
- Remove printMode variable and all related checks
- Delete _sendPrintPrompt method
- Simplify all methods to use ACP bridge exclusively
- Throw error on connection failure (no silent fallbacks)
- Remove try-catch fallbacks in injectSkills and injectSystemContext

This enforces the principle: One working method for everything, never fallbacks.

Author: lanmower