Add active energy metric and a simple weekly verdict tile

[isAdamBailey]

Summary

• Pull active energy burned (calories from movement) from Google Health as a second progress signal alongside weight, since exercise can improve while the scale doesn't move.
• Replace the grid of raw numbers on the dashboard with a single, glanceable "Better / Worse / Steady this week" tile: better if weight is down or energy is up, worse only if weight is up and energy didn't pick up the slack. BMI/category are still available via the chart's metric toggle.
• Saving a weight entry now triggers a background Google sync so new data (including active energy) shows up without a manual "Sync now".
• Add a "Reconnect" banner on the dashboard for when Google's test-app refresh token expires (every 7 days until the app is published) or is revoked.
• Fix a timezone bug in the weekly-grouping composable: date-only strings (like active energy's day field) were parsed as UTC midnight, which could shift into the wrong local week for negative-UTC-offset timezones.

Test plan

• go build ./..., go test ./..., golangci-lint run ./... all pass in backend/
• npm run lint, npx vue-tsc --noEmit, npm run test, npm run build all pass in frontend/
• Verified live: ran migrations against a real Postgres, logged in via magic link through Mailpit, created a weight entry, and hit the new /api/active-energy endpoint end-to-end
• Manually verify the dashboard UI in a browser (Active energy chart toggle, verdict tile, reconnect banner) — no browser automation tool was available in this session

🤖 Generated with Claude Code