refactor: bundle render args into RenderParams

[marksverdhei]

Draft — for your decision on the RenderParams judgment call (#3). Opened as a draft so you can see the concrete diff before committing to the API shape; not meant to merge without your go-ahead.

Groups the five shared pose/shading arguments (azimuth, altitude, zoom, light_dir, fg_override) into a RenderParams struct passed by reference:

pub fn render_frame(fb: &mut Framebuffer, mesh: &Mesh, params: &RenderParams)
pub fn render_frame_gpu(fb: &mut Framebuffer, pipeline: &RasterPipeline, ctx: &GpuContext, params: &RenderParams)

Pros

• render_frame 7 args → 3; render_frame_gpu 8 → 4. Drops render_frame_gpu's #[allow(clippy::too_many_arguments)] (the per-triangle rasterize_triangle allow stays — its args don't bundle).
• A named struct reads better at call sites than five positional floats.
• Pre-1.0 / pre-public is the cheapest time to change this signature.

Cons / why it's a judgment call

• API churn across ~6 call sites (done here).
• Only removes 1 of the 2 lint suppressions.
• My standing recommendation in Hivemind Maintenance Tasks Epoch 1 #3 was to defer this to M3 (when materials/lighting grow the param set) — this draft exists so you can weigh that against the concrete diff.

Verification: behavior-preserving — GPU/CPU output stays byte-identical (gpu_compare 0.00%), full suite green (41 tests), fmt + clippy -D warnings clean.

Merge if you like the shape; otherwise close and I'll keep the deferral note in #3.