Debug code behind compile-time flag

[opencode-agent]

The implementation is complete. Let me provide a summary:

Changes made to src/game/app.zig:

1. Added compile-time debug_build constant using Zig's builtin mode detection
2. Created DebugState packed struct to hold debug toggle state (lines 6-9)
3. Added debug_state: DebugState field to App struct (line 34)
4. Updated key handlers for 'u' (toggle shadows) and 'k' (cycle cascade) to use self.debug_state (lines 194, 198)
5. Wrapped debug shadow map visualization with if (debug_build) (line 357)
6. Wrapped debug stats UI (FPS, position, chunks, time, sun intensity) with if (debug_build) (lines 371-405)
7. Wrapped console debug output with if (debug_build) (lines 457-464)

Acceptance Criteria Status:

• Debug rendering code behind compile-time flag
• Release builds don't include debug code (all debug code is within if (debug_build) blocks)
• Debug builds still have full functionality

Closes #29

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[MichaelFisher1997]

/oc can you fix this, it fail to build in the runner

[opencode-agent]

Fixed the build failure by wrapping the debug key handlers (u and k keys) with if (debug_build). This prevents the debug_state fields from being accessed in release builds where they would be unused, causing compiler warnings/errors.

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