feat(#672): finish quick actions tts foundation

[lokhor]

Summary

Finish the remaining Quick Actions voice foundation work covered by #671 and #672, including the dedicated Voice settings surface for spoken-response controls.

Changes

• keep the shipped Quick Actions push-to-talk / offline Vosk baseline aligned with current issue scope
• add a shared VoiceOutputPreferences store in core:voice
• warm Android TextToSpeech when spoken responses are enabled
• add explicit TTS audio attributes and transient audio-focus handling
• make ActionsViewModel respect the spoken-response preference
• add a dedicated Settings -> Voice screen for spoken-response controls
• move the spoken-response toggle out of About
• update the authoritative spec and roadmap docs to reflect the current voice foundation state
• fix the pre-existing MemoryViewModelTest suspend stubs so feature:settings unit tests compile and run again

Testing

• :feature:chat:testDebugUnitTest --tests '*ActionsViewModelVoiceTest'
• :feature:settings:testDebugUnitTest
• :app:assembleDebug
• Manual device testing

Manual device testing

• confirmed Settings -> Voice shows Speak Quick Actions voice responses
• confirmed the toggle defaults on
• confirmed disabling it silences Quick Actions / QIR spoken responses
• confirmed re-enabling restores speech
• confirmed the current Quick Actions push-to-talk voice path works on device

Notes

• This PR stays within the current shipped voice surface: Quick Actions / QIR only.
• It does not add chat voice.
• The new Voice settings screen is intended to host future STT/TTS settings, engine choices, and voice model controls.

Related issues

Closes #671
Closes #672

[github-actions]

Debug APK ready

Download app-debug.apk

Commit: e0c4d26 - Build #1125

Updated on each push. Removed when PR is merged or closed.