Default homepage range to 7 days for faster initial load

[raychrisgdp]

Context

The homepage currently defaults to the 30-day range. For faster initial loading, change the default homepage view to 7 days.

Desired UX

• On first load, the 7d range pill should be active.
• Initial API calls should use days=7 by default.
• Users can still switch to 3d, 30d, 90d, All, or custom ranges.
• Existing explicit range behavior should not change after the user selects another range.

Implementation Notes

Likely touchpoints:

• templates/index.html
  • make the 7d pill active/aria-pressed="true"
  • make the 30d pill inactive/aria-pressed="false"
  • update the JS default state if it currently assumes 30
• Tests that assert default range or active pill state, if any.

Keep this as a small behavior-only change. Do not change available range options or backend range semantics.

Acceptance Criteria

• Homepage first render shows 7d selected.
• Initial dashboard fetches use days=7.
• Date range switching still works for all existing options.
• Tests are updated or added for the default active range.
• Existing overview/model/daily/history source labeling remains unchanged.