Change default map theme

### Description
Change default theme from OSM to https://www.maptiler.com/maps/#style=streets-v2

[Concise description]

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### Checklist
- **Does it need UI/UX design?**
- [ ] Yes. Describe the UI/UX requirements or attach a Figma link in the "Design" section.
- [ ] No
- **Does it need API design?**
- [ ] Yes. Specify the endpoints, methods, or data structures needed.
- [ ] No
- **Does it need design around state flow?**
- [ ] Yes. Outline the state flow requirements.
- [ ] No
- **Does it need a test plan?**
- [ ] Yes. Add the test plan as a comment in this task or attach the document.
- [ ] No
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### User Stories

- **As a** [user type],
**I want** [functionality],
**so that** [benefit].

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### Design

- **Figma**: [Insert URL]
- **Design Docs**: [Insert URL]

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### Dependencies

-

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### Additional Notes

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### Related Issues

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Locate the configuration or entry point that sets the default OSM map theme, then review how the map theme URL is applied. Done means new maps use MapTiler's streets-v2 style by default instead of OSM, with existing map behavior preserved.

Written by the indexing model from the issue text.