Giving chart planning explicit model controls

Helix separates the harness, the model, and the reasoning level used for chart planning. The default harness is the Codex-compatible path, while OpenPaths remains the gateway for current model routes and controlled fallbacks.

Fast planning uses GLM 5.3 DL Flash and full planning uses GLM 5.3. DeepSeek Experimental remains a compatibility fallback. Gemini is available as a model route, but is no longer treated as a separate harness.

Unknown selections normalize to safe defaults, older model names continue to resolve, and the deterministic renderer validates every proposed chart before it reaches the user.