feat: Add meter events query endpoint

[lajay-faith]

Closes #439

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Summary

Expose a query endpoint that pages through Soroban contract events filtered to a single meter ID. This lets the frontend display a full on-chain activity log without parsing raw event streams client-side.

Changes

• Added GET /api/meters/:id/events endpoint with pagination support
• Reuses event-fetching logic similar to payments.ts but filters by meter topic
• Returns structured event data with { events: [...], pagination: { page, limit, total } }
• Returns 404 when meter does not exist
• Added parseContractEvent helper function to parse Soroban events

Acceptance Criteria

• GET /api/meters/:id/events?page=1&limit=20&days=30 works
• Reuses event-fetching logic filtered by meter topic
• Returns { events: [...], pagination: { page, limit, total } }
• Returns 404 when meter does not exist
• Added /:id/events sub-route in meters.ts

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