Add Icing and Offside counters for statistics

[JRemitz]

Summary

Add Icing and Offside counters (per team, similar to Shots on Goal and Faceoffs) for statistics tracking.

Motivation

Users tracking full game statistics want icing and offside totals alongside the existing SOG and FO counters. Currently there is no way to record these events.

Requested Behavior

• Per-team Icing count (home + away)
• Per-team Offside count (home + away)
• Text file output (e.g. icing_home.txt, icing_away.txt, offside_home.txt, offside_away.txt) so users can surface them in OBS overlays
• Dock UI controls to increment/decrement
• Hotkeys for hands-free operation
• Persisted in JSON save/load
• Reset on new game

Acceptance Criteria

• scoreboard-core exposes icing/offside get/increment/reset API
• Files written to output directory
• Dock UI buttons + hotkeys
• Save/load round-trips the new fields
• 100% line coverage maintained on scoreboard-core.c

Reported via user feedback.