Add Category Navigator to Three.js

[nekomario28]

Summary

Continues #276 P2 by donating the existing 2D Category Navigator product semantics to the experimental Three.js renderer through a thin renderer adapter, without coupling Canvas and WebGL internals.

Three.js renderer adapter

• Runs after shared Local Graph and shared Search Context adapters.
• Exposes only the navigation boundary needed by the UI: admitted graph lookup, current mesh visibility, selected node id, select/clear selection, canvas focus and an evidence snapshot.
• Emits navigator change events from visibility and selection updates instead of polling the Three.js scene.
• Normal navigator selection changes camera/details selection only; it does not mutate Local Graph focus/depth scope.

Category Navigator behavior

• Reuses the existing category-navigator.css presentation rather than forking another design system.
• Lists only nodes currently visible after status + Local Graph + shared search projection.
• Owned repositories stay under their admitted owned category.
• Contributed repositories appear in a separate External contributions · not owned section; no fake category membership is created.
• Category and repository buttons select the corresponding Three.js mesh and toggle off when selected again.
• Search-driven disclosure/emphasis consumes window.ProjectMapSearchContext instead of introducing another text matcher.
• Status/search/Local Graph visibility changes re-render the navigator from the renderer adapter.
• The panel remains an accessible non-spatial route for 3D scenes where depth/occlusion makes direct raycast selection harder.

Gates

• postprocessor order fails closed unless Local Graph + shared Search Context have already run;
• generated Three.js and navigator runtimes receive Node syntax coverage and the Pages ESLint gate;
• attachment and runtime patching are idempotent;
• Chromium E2E verifies owned/external separation, repository/category selection identity, toggle-to-clear behavior, search/status visibility and that normal navigator selection leaves Local Graph node/edge scope unchanged;
• existing full Verify, twelve-preset comparison, Three.js search parity, 120/480-repository performance evidence and WebKit smoke remain enabled.

Selected/direct-search projected repository labels remain a separate P2 increment; this PR does not enable repository-wide DOM labels or global semantic-edge rendering.

Refs #276.