Setting: board orientation (home board on left or right)

From tester feedback (jholmertz, Discussion thread).

Allow the user to choose the board orientation — specifically, to place the
home board on the left side instead of the right, which is the current
default.

This is a display preference (not a change to the position itself), so it
belongs in Settings, alongside the board-style picker. It's a horizontal
mirror of the board layout, distinct from the existing vertical flip that
keeps the user (blue) at the bottom.

Scope to consider:
- Affects the board renderer (BGGBoardView / BGGBoardElements): tongue
arrangement, off-tray position, cube strip.
- Must apply consistently across all boards (Warm-up, Cluster, Training,
Workout, and the position browser).
- Pip-count input fields ("opponent" / "my") and any left/right wording in
explanations should still make sense after mirroring.
- Store the choice like other display preferences (NSUserDefaults), no
CloudKit needed.

Start by reading the existing board-style setting and the BGGBoardView/BGGBoardElements renderer, including how display preferences are stored in NSUserDefaults. Trace the layout across Warm-up, Cluster, Training, Workout, and the position browser. Done means the horizontal orientation preference mirrors the specified board elements consistently while keeping pip-count fields and explanation wording meaningful.

Written by the indexing model from the issue text.