Add pipe network layout example with legend, walls, outlines and FPS stats

[aka-blackboots]

Motivation

• Provide an architecture-consistent example that demonstrates Sweep (path + profile) usage for multi-branch pipe/MEP layouts with visual legend and contextual walls.
• Give users runtime controls for outlines, fat outlines and outline width, plus performance visibility via an FPS counter.

Description

• Added a new example HTML at main/opengeometry-three/examples-vite/operations/pipe-network-layout.html that builds four pipe types using Sweep + Rectangle profiles, adds cuboid walls, and renders a side-panel legend.
• Integrated UI toggles for showOutlines, fatOutlines, outlineWidth, showWalls, and showStats following the existing examples' control binding and scene-replacement patterns.
• Wired Three.js Stats (three/examples/jsm/libs/stats.module.js) to show FPS and added console logging of a serialized pipe network config whenever controls change.
• Registered the example in the examples index by updating main/opengeometry-three/examples-vite/index.html (operations count bumped to 9) and added a handoff document at AI-DOCs/2026-03-11-pipe-network-layout-example.md.

Testing

• Ran npm --prefix main/opengeometry-three run build-example-three, which failed due to missing generated wasm artifacts (main/opengeometry/pkg/opengeometry_bg.wasm), so Vite could not resolve wasm imports (build failed).
• Started the dev server with npm --prefix main/opengeometry-three run dev-example-three -- --host 0.0.0.0 --port 4173, which launched but produced Vite import-resolution errors for the same missing pkg artifacts so the example could not fully initialize.
• Captured a headless screenshot of the example route via Playwright to validate the page loads to the dev server (screenshot saved as an artifact), and observed the Vite overlay/errors in the running dev server logs.
• Committed the changes (new example, index update, and AI handoff note); full runtime validation requires the generated OpenGeometry pkg/wasm artifacts to be present (documented in AI-DOCs/2026-03-11-pipe-network-layout-example.md).

---

Codex Task