fix: replace chat identity popovers with profile panel

[rogerchappel]

Summary

• replace message-level identity popovers with one top-level profile surface
• render as a right-side desktop profile pane and a full-height mobile slide-up panel
• keep chat name/avatar clicks as the trigger without covering message text

Verification

• pnpm typecheck
• git diff --check origin/main..HEAD
• push hook ran pnpm typecheck and pnpm build