fix(voice): reclaim the mobile conversation viewport

[JulioMCruz]

Summary

• remove duplicate mobile voice and chat headings, leaving one compact call header/action
• strengthen compact Conversation/Settings tabs and expand the bounded conversation viewport
• keep the history flexible and composer visible while preserving desktop behavior and all voice privacy policies

Validation

• focused voice/chat suites: 23/23
• full suite: 362/362
• typecheck and changed-file lint
• production build: 51 routes
• diff check and scoped secret scan clean

Post-deploy acceptance will inspect the real authenticated Bragi page at 390x844 in both Conversation and Settings without starting a call.