Summary

• Adds a "Use test data" switch in Settings > Developer (visible only in debug builds)
• When enabled, replaces real sensor data with generated test data on both the Dashboard and Activities screens
• Each date produces a unique but deterministic pattern using date-seeded randomization with 7 day-type archetypes (commute, active, rest, long-run, mixed, afternoon-heavy, morning-heavy)

Test plan

• Install debug build, open Settings, verify "Developer" section appears at the bottom
• Toggle "Use test data" on — Dashboard should show fake steps, weekly chart, and transitions
• Navigate to Activities screen — should show generated sessions and step graph data
• Navigate between dates in Activities — each day should look different
• Toggle "Use test data" off — both screens should revert to real data
• Build a release APK and verify the Developer section is not visible

🤖 Generated with Claude Code