fix(tests): update test_metrics.py assertions for renamed Prometheus metrics after #264 #283

Summary

Two assertions in tests/test_metrics.py permanently fail after the metrics rename in fix #264.
Line 60 asserts 'rag_routing_latency_ms 200.0' in body -- FAILS (metric renamed to rag_routing_latency_ms_sum / _count).
Line 63 asserts 'rag_fallback_rate 0.0' in body -- FAILS (rag_fallback_rate gauge was removed entirely).

Root cause

Fix #264 changed render_prometheus() to emit rag_routing_latency_ms_sum and rag_routing_latency_ms_count, and removed rag_fallback_rate. The test was not updated.

Fix

tests/test_metrics.py lines 60-63: update assertions to new metric names (rag_routing_latency_ms_sum, rag_routing_latency_ms_count). Remove or update rag_fallback_rate assertion.

Impact

CI fails on every run. All PRs are blocked.