feat(studio): polish video editor UI and interactions

[jhe009809-hue]

Summary

• Improved timeline and layer interactions, including resizable layer panels and clearer hover states.
• Updated Ask AI, toolbar icons, loading indicators, and accent colors to match the latest Figma designs.
• Standardized desktop typography and improved dark-mode text contrast, selection, hover, pressed, focus, and disabled states.
• Added complete English and Chinese localization for the voice panel, including preset names, descriptions, statuses, errors, and accessibility labels.
• Updated automated experience flows and regression coverage for the new Studio behavior.

Validation

• App and Studio TypeScript checks passed.
• Focused UI, animation, typography, and voice tests passed.
• Studio production build passed.
• Maintainability audit passed with no errors or warnings.
• Verified the updated animation, dark-mode, and English voice-panel experiences in the development client.