feat(blame): add inline blame display mode option

[CalvinAllen]

Summary

• Replaces the unimplemented ShowOnHoverOnly boolean with a new InlineBlameDisplayMode enum setting with three modes:
  • Always — show inline blame on all visible lines (existing default behavior)
  • CurrentLine — show inline blame only on the current caret line
  • Hover — show inline blame only when the mouse hovers over a line
• Exposes the new setting in Tools > Options > Git Ranger > General under the Display category

Resolves #74

Test plan

• Verify Always mode shows blame on all lines (existing behavior unchanged)
• Verify CurrentLine mode shows blame only on the caret line, updating as the caret moves
• Verify Hover mode shows blame only on the line under the mouse cursor, clearing when the mouse leaves the editor
• Verify switching between modes in Tools > Options takes effect immediately
• Verify the setting persists across VS restarts