Bugfix/activity UI sync alerts - #61

Summary

Multiple bugs fixed:

• Ring card values never truncate to "10,…" anymore
• Garbage values can no longer render.
• Coach notifications now wait for sync.
• Sleep page AI coach card moved under the sleep data.

Features:

• Low-battery alerts (<20% and <10%, default ON per your choice)
• Workout history groups workouts under dates
• Graph for battery drainage

Related issues

Closes #53, #25 & #26

Type of change

• 🐛 Bug fix (non-breaking change that fixes an issue)
• ✨ New feature (non-breaking change that adds functionality)
• 📟 New / improved wearable support (BLE driver layer)
• 🤖 Coach / LLM change (tools, prompts, orchestration)
• 🎨 UI / DesignSystem change
• 🧹 Refactor / chore (no behavior change)
• 📝 Docs only
• ⚠️ Breaking change (existing data, settings, or APIs change)

How was this tested?

Tested on iPhone 16 Pro

• Added / updated unit tests (PulseLoopTests)
• Ran the test suite locally (⌘U in Xcode)
• Tested on a physical device with a real ring — model:
• Tested with demo data (-seedDemo YES, no hardware)
• N/A (docs / non-code change)

Privacy & data

• This change does not send health data off-device without explicit user action.
• No secrets, API keys, or personal data are committed.
• N/A

Checklist

• My code follows the project's style (SwiftLint passes).
• I ran the tests and they pass.
• I updated docs / README where relevant.
• I read the Contributing guide.