Add endpoint-level latency budgets and SLO guidance

[robertocarlous]

Why
The system already tracks HTTP and analytics latency, but the team still needs explicit performance targets to judge whether a slowdown is acceptable or not.

Acceptance criteria

• Define latency targets for critical public and internal endpoints.
• Tie the targets to existing metrics and dashboard panels.
• Document how to interpret sustained SLO misses.

[femiolutayo]

I want to apply for this issue because defining clear latency budgets and service-level objectives is essential for maintaining reliable backend performance and making data-driven operational decisions. With my experience working with backend systems, monitoring, and performance analysis, I can establish realistic endpoint-level targets, map them to existing metrics and dashboards, and document actionable guidance for identifying, investigating, and responding to sustained SLO violations.