feat: implement event-indexer improvements (#809, #818, #815, #811)

[ubermensh-323]

Closes #809 : Add GET /matches?status= endpoint filtered at DB layer
Closes #818 : Add limit/offset pagination to GET /events/:match_id (default 100)
Closes #815 : Validate CONTRACT_ESCROW is a valid 56-char Stellar address on startup
Closes #811 : Add DB ping (SELECT 1) to GET /health, return {db: ok/error}

• Update docs/EVENT_INDEXER_API.md with new response schemas

Summary

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Related Issue

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What changed

• Contracts:
• Tests:
• Docs:
• Events / API / storage:

Verification

• What did you run to verify this change?
  • cargo test -p escrow
  • cargo test -p oracle
  • cargo fmt
  • cargo clippy

Checklist

• I added or updated tests covering this change.
• I updated documentation or confirmed no docs update is needed.
• I confirmed any event/API/storage changes are documented and backward-compatible.
• I manually verified the contract or CLI behavior where applicable.
• I linked this PR to the related issue.
• I included notes on any TTL or storage assumptions affecting contract state.

Notes

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