feat(assistant): refresh continuous-call UI with live bubbles

[gac0812]

Summary

• 长对话（免提）全屏层改成气泡对白在上、声纹球在下；用户句右气泡、助手句左气泡。
• 超出一屏后列表可以上滑回看；短列表仍贴在声纹球上方。
• 去掉「打断当前对话」按钮；左上角只收起，底部红色「结束对话」才挂断。
• 不包含登录、日历首页、按住说话和日程写入等非长对话 UI 改动。
• 阅读时是否贴底、以及「查看最新」入口不在本次范围，见 feat(ui): 长对话回看时保持阅读位置 #313。

Closes #309

Test plan

• 点底部电话进入长对话：对白在上、声纹球在下
• 用户句右气泡、助手句左气泡；正在说的一句可带波形
• 本通多轮超出一屏可上滑回看
• 左上角收起不挂断；点圆圈暂停/继续；「结束对话」挂断
• 没有「打断当前对话」按钮

Verification

cd frontend
npx jest --runInBand tests/unit/features/assistant/presentation/VoiceCallScreen.test.tsx tests/unit/features/assistant/presentation/usePinnedTranscriptScroll.test.ts tests/unit/features/assistant/presentation/useAssistantConversation.test.tsx tests/unit/features/assistant/presentation/AssistantVoiceOverlay.test.tsx tests/unit/features/assistant/application/AssistantContinuousConversationService.test.ts tests/unit/features/assistant/application/AssistantConversationService.test.ts tests/unit/screens/HomeScreen.test.tsx

本地结果：Test Suites: 7 passed，Tests: 80 passed。

覆盖要点：

• 气泡对白、收起/挂断/暂停、声纹球音量与跳动（iOS / Android / Web）
• 超长列表可滚动、短列表贴底
• 本通 getMessages() 追加用户句/助手句，流式 pending，新通话清空
• 按住说话 getMessages() 仍为空数组

设计对照

截图由作者提供，不进源码树，只作为 Review 附件：

改前（状态文案列表 +「打断当前对话」）：

改后（气泡对白 + 底部声纹球）：

[codecov]

Codecov Report

❌ Patch coverage is 96.03175% with 5 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
...lication/AssistantContinuousConversationService.ts	92.30%	2 Missing ⚠️
...eatures/assistant/presentation/VoiceCallScreen.tsx	97.01%	2 Missing ⚠️
...s/assistant/presentation/AssistantVoiceOverlay.tsx	80.00%	1 Missing ⚠️

📢 Thoughts on this report? Let us know!

[fennoai]

Reviewed the fixed 612955df0cd65f54006952918c98159a609a4799...f224033191998f83120b736f07970ed95e98888e diff across the continuous conversation service, application port/domain changes, overlay, voice-call screen, pinned transcript scrolling, and associated tests. I found no PR-introduced correctness, security, performance, or maintainability issue that meets the reporting threshold.

Verification: git diff --check passes. The requested Jest command could not run in this workspace because the local frontend/node_modules does not contain the jest-expo preset; npm exec also resolved a standalone Jest version without the repository dependencies, so no test result is inferred from that attempt.

[gac0812]

/android-preview