Address remaining ASB review cleanups

[haasonsaas]

Summary

• reject non-finite rate limit config values and cover them in tests
• bound budget exhaustion metric labels by connector kind instead of proxy handle
• close redis clients on bootstrap error paths and prebuild the HTTP rate-limit middleware once

Testing

• go test ./cmd/asb-api ./internal/app ./internal/bootstrap ./internal/api/httpapi -count=1
• go test ./... -count=1

[cursor]

PR Summary

Medium Risk
Moderate risk due to behavior changes in config validation, HTTP middleware wrapping, and Prometheus metric label schema (may break dashboards/alerts). Runtime impact should be limited, but regressions could affect rate limiting, readiness startup, or observability.

Overview
Tightens HTTP server configuration validation by rejecting non-finite ASB_HTTP_RATE_LIMIT_RPS values (NaN/±Inf) and adds test coverage for these cases.

Reduces metric label cardinality by changing asb_budget_exhaustion_total to label by connector_kind instead of per-proxy handle, updating the service recording sites and tests accordingly.

Cleans up infrastructure wiring by prebuilding the HTTP rate-limit middleware once in httpapi.Server (instead of per request), and ensuring Redis clients are closed on bootstrap error paths; redisPoolStats is narrowed to accept *redis.Client.

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