feat: Add Prometheus metrics for indexer and API

[cypriannwokolo2-creator]

Description

Add comprehensive Prometheus metrics for monitoring system health and performance.

Requirements

• Add events_processed counter
• Add events_failed counter
• Add cursor_lag gauge
• Add db_write_latency histogram
• Add reconciler_runs counter

Acceptance Criteria

• All metrics exposed via /metrics endpoint
• Grafana dashboard created
• Alerts configured for critical metrics
• Documentation for all metrics

Priority

Medium

[acejayl]

@acejayl has applied to work on this issue as part of the Stellar Wave Program's 8th wave.

Instrumentation is additive so it can't break the paths it watches, which makes it a good one to land quickly. Plan: a single metrics module registering the five listed metrics, events_processed and events_failed as counters, cursor_lag as a gauge, db_write_latency as a histogram, and reconciler_runs as a counter, then increment them at the real call sites in the indexer and API rather than wrapping everything. Expose them on a metrics endpoint in the standard Prometheus text format so it scrapes without extra config. I'd pick histogram buckets that suit actual DB write times instead of the library defaults, since default buckets usually make write latency useless. Happy to take it on.

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[olayiwola-web]

@olayiwola-web has applied to work on this issue as part of the Stellar Wave Program's 8th wave.

I have the background for this kind of change and I’ll implement it against the listed requirements and acceptance criteria. PR will align with the repo. Assign me and I’ll begin.

ℹ️ Repo Maintainers: To accept this application, review their application or assign @olayiwola-web to this issue.

[ybmahq]

@ybmahq has applied to work on this issue as part of the Stellar Wave Program's 8th wave.

Hi, I'd like to work on this issue.

I have hands-on experience with backend development, databases, and API design, as well as frontend work with React and modern CSS. I write tested, maintainable code and enjoy contributing to open source projects.

I've looked into this issue closely and I'm confident in my ability to deliver a high-quality implementation here.

Please assign this issue to me, I'd be happy to contribute.

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[linesofcodes0-cloud]

@linesofcodes0-cloud has applied to work on this issue as part of the Stellar Wave Program's 8th wave.

I'm a full-stack developer and I'd like to take this issue.
I understand the requirements and will follow the existing project structure, keep the implementation clean, and include proper tests where applicable.

ETA: 1–3 days (depending on scope)

ℹ️ Repo Maintainers: To accept this application, review their application or assign @linesofcodes0-cloud to this issue.

[Sheebazz]

@Sheebazz has applied to work on this issue as part of the Stellar Wave Program's 8th wave.

Hi Maintainer, I’ve reviewed the issue and would like to work on it. I can add the required Prometheus metrics for the indexer and API, expose them through the metrics endpoint, and set up the related Grafana dashboard and alerts.

I’ll also document the metrics and make sure the implementation is covered by the appropriate tests.

Please consider assigning this issue to me. Thank you.

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