Refine conversation streaming and shared UI controls

[jhe009809-hue]

Summary

This PR improves conversation readability and streaming behavior, and aligns plugin and video Studio controls with the shared UI system.

• Align conversation content with the composer, standardize typography and spacing, and limit image preview size with expand/collapse controls.
• Refine generated file cards with compact thumbnails, thin borders, white backgrounds, and lightweight actions.
• Keep streamed answers in a stable result area, apply pulse animation only to the active processing step, and preserve completion, retry, and interruption states.
• Add shared Lucide icons in S/M/L sizes and support icon-and-text buttons at 28/32/36px heights, defaulting to 32px.
• Reuse shared controls across video Studio while preserving upstream functionality.

Validation

• App, shared UI, and Studio type checks passed.
• 151 focused tests passed.
• Fraimz passed: 24 conversation frames, 24 video UI frames, and 14 shared UI frames.
• git diff --check passed.
• The commit hook could not run because lefthook was unavailable; the checks above were run manually.