[codex] add texture storage guardrails

[mikechaves]

Summary

• Add shared material storage budget helpers for embedded texture payloads.
• Show the current draft texture storage footprint in the editor texture panel.
• Warn or block projected material saves before the local library becomes too large for browser storage.
• Block JSON imports that would push the local material library over the storage budget.
• Fix mobile spacing so the collapsed sidebar menu button does not overlap the first editor heading.

Validation

• npm run quality:full
• Browser QA at http://127.0.0.1:5173/ on desktop and mobile 390x844
• Desktop and mobile console checks showed no warnings or errors

Notes

This improves feedback and prevents over-budget local saves/imports. It does not yet compress or downscale texture images automatically.

[gemini-code-assist]

Code Review

This pull request introduces a material storage budget system to manage local browser storage limits. It includes a new utility for analyzing and summarizing texture storage, UI updates to display storage usage in the TextureControls component, and logic to warn or block users when saving or importing materials that would exceed defined thresholds. Additionally, it adds comprehensive unit and E2E tests to ensure the storage limits are correctly enforced and reported. I have no feedback to provide as there were no review comments.