Remove render_system.zig wrapper, inline to app.zig

[MichaelFisher1997]

Parent Issue

Part of #26 (Full Codebase Audit v3)

Category

Quick Win (0.5-1 day)

Problem

render_system.zig is a thin wrapper that adds indirection without significant value. It holds both RHI and raw shader refs creating dual state management.

Current State

• RenderSystem struct in src/game/render_system.zig
• Holds RHI, atlas, shaders, atmosphere, clouds, shadow_map
• App creates and uses RenderSystem

Proposed Solution

Inline RenderSystem fields directly into App or have RHI own these resources directly.

Files to Modify

• src/game/render_system.zig (delete)
• src/game/app.zig (absorb functionality)

Risk

Low - simple refactor, no behavior change

Acceptance Criteria

• render_system.zig deleted
• All functionality preserved in app.zig or RHI
• No regression in rendering

[MichaelFisher1997]

/oc can you give this a shot and put it on a branch called "stage"

[opencode-agent]

Validation Failed: {"resource":"PullRequest","code":"custom","message":"No commits between main and opencode/issue28-20251224045520"} - https://docs.github.com/rest/pulls/pulls#create-a-pull-request

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[opencode-agent]

error: src refspec opencode/issue28-20251224123747 does not match any
error: failed to push some refs to 'https://github.com/MichaelFisher1997/ZigCraft'

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[MichaelFisher1997]

/oc can you give this a shot

[opencode-agent]

The refactoring has already been completed. The render_system.zig file doesn't exist in the codebase, and app.zig already contains all the rendering-related fields (rhi, shader, atlas, atmosphere, clouds, shadow_map) inline. The issue is resolved.

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