Implement Tab Navigation with Turbo Frames

[frogr]

Acceptance Criteria

• Six tabs: Game, Inventory, Quests, Map, Stats, Perks
• Tab content loads via Turbo without page refresh
• Active tab persists in session storage
• Keyboard shortcuts (I=inventory, J=quests, M=map)

Technical Requirements

• Create tabs_controller.js Stimulus controller
• Each tab loads content into turbo_frame_tag "game_content"
• Routes: /game/main, /game/inventory, /game/quests, etc.
• CSS active state with green glow effect