feat(deps)!: migrate from fiber v2 to fiber v3

BREAKING CHANGE: upgrades the HTTP framework from gofiber/fiber/v2 to gofiber/fiber/v3, and gofiber/websocket/v2 to gofiber/contrib/v3/websocket.

- Handlers now take fiber.Ctx (interface) instead of *fiber.Ctx. - DisableStartupMessage moved from fiber.Config to fiber.ListenConfig on the proxy/api/monitoring Listen calls. - cors AllowOrigins is now []string; c.BodyParser -> c.Bind().Body(). - app.Test takes fiber.TestConfig instead of an int timeout (tests updated). - WebSocket swapped to contrib/v3/websocket (same Conn/New/Config/IsCloseError/IsWebSocketUpgrade API; Conn.Query preserved). - Adopts fasthttp v1.71.0 (pulled by fiber v3), resolving the v1.71 Host-header enforcement that broke the prior pinned-v1.69 workaround.

fix(connpool): the background keep-alive goroutine no longer reads the mutable global cfg (captures HostGraphQL/HealthcheckGraphQL at pool creation). Under v3 timing it raced with parseConfig/test cfg reassignment; go test -race ./... is now clean (0 data races).

test: make the circuit-breaker cache-fallback and request-coalescing integration tests deterministic (cache TTL outlives the retry loop; coalescing asserts against a measured single-request baseline instead of a hard-coded count); drop the flaky timing-ratio assertion in TestTimingAttackResistance (constant-time guarantee comes from subtle.ConstantTimeCompare, not wall-clock timing).

Verified: go build, go vet, golangci-lint (0 issues), go test -race ./... (all packages pass, 0 races), govulncheck (no vulnerabilities). App + dashboard + WebSocket verified live under v3 in single-node and cluster modes.

debug_routing.go

@@ -4,7 +4,7 @@ import (
 	"fmt"
 	"strings"
 
-	fiber "github.com/gofiber/fiber/v2"
+	fiber "github.com/gofiber/fiber/v3"
 	"github.com/graphql-go/graphql/language/ast"
 	"github.com/graphql-go/graphql/language/parser"
 	"github.com/graphql-go/graphql/language/source"
@@ -20,7 +20,7 @@ import (
 //   - Automatic detection of mutations routed to wrong endpoints
 //
 // To enable: Set LOG_LEVEL=DEBUG and restart the proxy
-func debugParseGraphQLQuery(c *fiber.Ctx, query string) {
+func debugParseGraphQLQuery(c fiber.Ctx, query string) {
 	if cfg == nil || cfg.Logger == nil {
 		return
 	}