Add alerts, docs, and logging improvements

[parkerwinner]

This PR enhances the server with comprehensive environment documentation, duplicate alert validation, structured logging utilities, and indexer startup observability.

Changes

Documentation:

• Added complete environment variables reference with all required and optional variables grouped by category
• Included security notes for credentials requiring regular rotation
• Documented types, defaults, and descriptions for all config vars

Price Alerts:

• Implemented duplicate alert detection returning 409 when identical active alert exists
• Added integration test verifying duplicate prevention and database state
• Ensures only one active alert per creator/wallet/price/direction combination

Logging Utilities:

• Added ledgerLogContext helper for consistent structured logging of ledger sequence and timestamp
• Formats timestamp as ISO 8601 UTC across all log entries
• Includes comprehensive unit tests

Indexer Observability:

• Added startup sync state logging showing last processed ledger and network lag
• Calculates estimated catchup time based on 5 seconds per ledger
• Emits warning for fresh starts with no processed ledgers
• Includes full unit test coverage

Testing

All new features include integration or unit tests verifying correct behavior and error handling.

Closes #542
Closes #541
Closes #540
Closes #538

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@parkerwinner Great news! 🎉 Based on an automated assessment of this PR, the linked Wave issue(s) no longer count against your application limits.

You can now already apply to more issues while waiting for a review of this PR. Keep up the great work! 🚀

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