Add inline research composer and clickable previews

[MaggieAppleton]

Summary

• render the research question composer inline at its durable document position
• preserve keyboard, IME, request identity, placement recovery, and focus behavior
• make ready research previews accessible full-card actions while hiding source lists

Verification

• bun run fix
• focused unit tests: 94 passed
• focused Playwright research specs: 10 passed
• bun run types
• bun run ci
• git diff --check

Generated docs/superpowers/plans and docs/superpowers/specs files are excluded.