Added comprehensive bug regression test that demonstrates:
1. The bug scenario (old implementation using startsWith() fails)
2. The fix works (new implementation using includes() passes)
Test covers:
- Terminal without image support scenario (bug trigger)
- Both Kitty and iTerm2 image protocols
- Very long lines (300KB+) matching crash scenario
- Integration with tool execution scenarios
- Negative cases (no false positives)
All 347 tests pass including 12 new bug regression tests.
