feat(parametric): add design tree viewer

[techfowl]

Summary

Adds a lightweight design tree for annotated parametric OpenSCAD artifacts.

The viewer now includes a collapsible design-tree drawer. Selecting a node filters linked parameter controls on desktop and mobile. Generated and edited artifacts also populate designTree metadata by parsing @cadam-node comments.

Closes #139
Related to #62

What changed

• Added shared DesignNode artifact metadata.
• Added @cadam-node comment parsing in shared/designTree.ts.
• Added a reusable design tree panel.
• Added a compact viewer drawer overlay.
• Shared selected-node state between viewer, desktop parameters, and mobile parameters.
• Added fallback parsing when older artifacts have annotated code but no populated tree.
• Updated parametric code generation guidance to emit CADAM design-tree annotations for important parts, operations, and assemblies.

Out of scope

This PR does not implement mesh/viewport click selection. That requires node-to-geometry mapping from generated source to compiled mesh output and should be handled separately.

Test plan

• npm run typecheck
• npm run lint — passes with existing warnings in unrelated files
• npm run build
• npm run lint:supabase

Manual checks still needed before marking ready for review:

• Annotated artifact shows viewer tree button with count.
• Opening drawer shows nested tree rows.
• Selecting a node filters desktop parameter controls.
• Clearing selection restores all parameters.
• Unannotated artifact opens drawer empty state.
• Mobile preview drawer opens and node selection filters mobile controls.
• Existing rendering, orbit controls, download controls, and compile loading overlay continue to work.

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Summary by cubic

Adds a design tree viewer for annotated OpenSCAD models. Selecting a node filters parameters, and artifacts now include designTree metadata parsed from @cadam-node comments.

• New Features
  • Parse @cadam-node comments into DesignNodes in @shared/designTree and attach designTree to artifacts.
  • Viewer gets a compact drawer with node count; selection is shared with desktop and mobile parameter panels.
  • Parameter panels add a Tree view and filter controls by the selected node; Clear restores all parameters.
  • Fallback parsing when older artifacts have annotations but no designTree.
  • Updated code-gen prompt to emit CADAM design-tree annotations for parts, operations, and assemblies.

^{Written for commit 4b3fbdc. Summary will update on new commits.}

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