Request: add explicit pre-flight warnings + agent best-practices for complex visual/3D workflows

### Summary
When using agentic coding workflows for complex visual projects (Three.js/Vite, scene-heavy UIs), users need an explicit pre-flight warning and setup checklist before agents begin making scene changes.

### Problem
In ambiguous scene contexts, agents may make valid-but-wrong assumptions (placement, camera/framing, flow mapping, asset control hierarchy). This can cause large time loss and repeated rework, especially when no project-specific guardrails are initialized first.

### Requested product behavior
Please add a default **precautionary warning / best-practices notice** before major scene edits, including:

1. Confirm project intent before coordinate/placement edits.
2. Recommend enabling a dev scene inspector first (object selector, transform/material/animation, keyframe, projection, source-apply).
3. Warn that ambiguous instructions (e.g., "build a 1000m curve camera") require explicit constraints.
4. Encourage diagnostics-first steps (visibility/frustum/material/clip state) before mutation.
5. Suggest setup of explicit logging/functions for fallback behavior.
6. Warn that runtime edits should translate back to source (JS/CSS/HTML), not remain ephemeral.
7. Include a legal/operational disclaimer for potential productivity loss from ambiguous agent assumptions.

### Why this matters
Professional teams often avoid these pitfalls by preconfiguring IDE/engine/pipeline tools. Agentic workflows are different and need first-class safety rails to avoid expensive regressions in real projects.

### Suggested UX
A lightweight "Complex Visual Workflow Detected" prompt with checkboxes:
- Require coordinate-confirmation for spawn/root transform changes
- Enable diagnostics mode first
- Initialize scene inspector utilities
- Enable guarded render-loop integration for tool failures
- Enable one-click source sync for interactive edits

This would materially improve reliability and user trust for complex scene development.

Nell’issue non sono indicati file o test. Inizia trasformando il prompt e la checklist proposti «Complex Visual Workflow Detected» in criteri di accettazione espliciti, quindi individua la superficie UX pertinente di Copilot Language Server; il lavoro è completato quando l’avviso viene visualizzato prima delle modifiche importanti alla scena e copre le misure di salvaguardia e il disclaimer elencati.

Scritto dal modello di indicizzazione a partire dal testo della issue.