Add ghost text wrapping for inline suggestions

[FuJacob]

Summary

• Adds a dedicated ghost suggestion layout helper that wraps overflowing suggestion text onto additional overlay lines instead of letting it run past the focused input frame.
• Threads overlay geometry through coordinator, presenter, overlay state, and controller so the first line can start at the caret while wrapped lines align to the input frame's left edge.
• Updates presentation and session tests to cover wrapped layout, overlay geometry, and acceptance behavior with the new state shape.

Validation

• swiftlint .
  • Found 0 violations, 0 serious in 78 files.
• git diff --check origin/main...HEAD
  • Exit 0.
• xcodebuild test -scheme tabby -destination 'platform=macOS' CODE_SIGNING_ALLOWED=NO
  • TEST SUCCEEDED; 151 tests, 0 failures.

Linked issues

Refs #94

Risk / rollout notes

• This is an approximate visual wrapping pass based on available caret/input geometry and observed character width. It improves overflow behavior, but it does not fully solve the follow-up bug where some host editors reflow accepted text before AX exposes the refreshed caret/text-node geometry.
• The unsigned test run still prints the existing llama/Metal shutdown assert after XCTest finishes, but xcodebuild exits successfully and reports TEST SUCCEEDED.