Comment/doc truth pass: purge painter-era and double-buffer-era staleness

Comment/doc truth pass: purge painter-era and double-buffer-era staleness

Code comments/javadoc now match the z-buffer, triple-buffered reality:
- RenderAggregator class javadoc (was painter's algorithm), ctor slot docs
- ViewPanel frameContexts/frameParity comments (was double-buffer/parity)
- RenderingContext depth comment (dropped dead -Daukio.zbuffer knob and
  'Null in classic painter mode' — depth is always allocated)
- TexturedTriangle/ShapeCollection/package-info: slot ranges 0..2,
  javadoc links retargeted off deleted painter span writers
- AGENTS.org: removed dead BSP-painter and Agentic-development doc links,
  added Depth buffer doc, LightmappedCompositeShape + TriangleMeshBlock
  to the class catalog, render-pipeline overview now describes the
  radix-sort + two-pass z-buffer flow
- TODO.org: dropped completed 'Add 3D mouse support' (SpaceMouse exists)

No behavior change.