fix: restore extension popup width

[sonson0910]

What changed

• restore the extension popup's designed 380px minimum width
• render Markdown emphasis in AI Mnemonic / Memory Hook content
• restore the original mobile nav styling, while keeping the dock visible through iPad portrait (lg:hidden)
• give the desktop LIBRARY: … CARDS status strip a raised surface and visible edge
• bump the extension release metadata to 1.6.3

Verification

• npm run lint
• targeted Vitest UI tests (12 passing)
• npm run build
• npm run extension:check
• npm run extension:build
• git diff --check

Fixes the reported extension width, mnemonic formatting, footer contrast, and iPad navigation regressions.