[Feature]: Investigate observability alternatives to Sentry

[CaseyHoover]

Problem / motivation

After removing Sentry (#110, follow-up to #109) the project will have no error tracking, no performance monitoring, and no log aggregation in production. We still want those capabilities — we just don't want them from Sentry. Need to pick a replacement (or deliberately decide "nothing for now") before any new SDK lands.

Constraints to weigh:

• Self-hostable preferred but not required
• Must not have the same dev-server pathology (`@sentry/nextjs` 10.x hangs undici TCP connects ~10s for some IPs in dev, see [Bug]: GitHub OAuth callback consistently slow (~10-14s) in dev #109)
• Cheap or free at our scale (small SaaS skeleton)
• Plays well with Next.js 16 RSC / instrumentation.ts and Hono on the API side
• TypeScript-friendly

Proposed solution

Produce a written comparison of viable options and a recommendation. At minimum cover:

1. Errors / traces / logs as one product
   • Sentry alternatives: GlitchTip (self-hosted, Sentry-protocol compatible), HyperDX, Highlight.io
   • OpenTelemetry → Honeycomb / Grafana Cloud / Tempo + Loki
2. Roll-our-own tier
   • Pino + log shipping + Vercel/Render built-ins
   • Just `onRequestError` from Next + Hono error middleware → external collector
3. Do nothing for now — accept no monitoring until product-market fit demands it. Document the gap.

For each: dev-mode overhead, vendor lock-in risk, cost at low traffic, integration effort, what we'd lose vs Sentry today.

Deliverable: an ADR-style doc (or just a comment on this issue) recommending an option, then file an implementation ticket.

Alternatives considered

• Skipping the investigation and re-introducing Sentry behind a dev gate — rejected; want a clean break, see [Feature]: Remove Sentry from the application #110.

Affected area

cross-cutting / unsure

Additional context

• Diagnosis thread: [Bug]: GitHub OAuth callback consistently slow (~10-14s) in dev #109
• Removal ticket: [Feature]: Remove Sentry from the application #110