[Feature] Add ASCII art banner to startup output

[spejman]

Summary

• Added ASCII art banner displaying "imploid" at the top of startup output
• ASCII art appears above the version line as requested
• Automatically respects --quiet flag (suppressed when quiet mode enabled via existing orchestrator logic)
• Updated tests to verify ASCII art inclusion

Implementation Details

• Added ASCII_ART constant to src/lib/startupBanner.ts:3-10
• Modified buildStartupBanner() function to prepend ASCII art to output array
• Updated both existing tests in tests/startupBanner.test.ts to verify ASCII art is present
• No new dependencies added (hardcoded approach as recommended in issue)

Test Plan

✅ Unit tests passing (2/2 tests in startupBanner.test.ts)
✅ Manual testing complete:

• Basic flow: Verified ASCII art appears above version line
• Quiet mode: Confirmed --quiet flag properly suppresses banner (via existing orchestrator.ts:320 logic)
• Version display: Verified version and description info still appear correctly after ASCII art
• Integration: Verified ASCII art works correctly with normal startup

Files Modified

• src/lib/startupBanner.ts - Added ASCII_ART constant and prepended to banner output
• tests/startupBanner.test.ts - Updated tests to verify ASCII art inclusion

Resolves #6

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