Move hardcoded Lagos coordinates to a configurable default

[snowrugar-beep]

• Problem Statement. Map.tsx initializes useState<[6.5244, 3.3792]>
  — hardcoded Lagos. Privacy and UX issue.
• Why it matters. Defaulting to a precise city pin is a
  privacy leak when users land on /map without consent.
• Expected Outcome. Map defaults to a private "world view" (zoom
  2); the user's first geolocation is opt-in via a banner.
• Acceptance Criteria.
  1. Initial state zoom=2 center=[20,0].
  2. "Use my location" banner; clicking issues permission prompt.
• Files / Modules. Frontend/src/components/map/Map.tsx,
  Frontend/src/components/map/LocationBanner.tsx new.
• Difficulty. Easy.
• Effort. 1 day.
• Labels. frontend, privacy, good first issue.

[theFirstCodeManiac]

Hi, maintainer. I'd love to work on this issue because I have the required experience. I'd be thrilled if it were assigned to me. Thank you.

[grantfox-oss]

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Next steps:

1. Open a Pull Request referencing this issue (e.g., Closes #147)
2. Your PR will be reviewed by the VertexChainLabs maintainers

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