fix: code compliance audit and fix across all services

NestJS (6 services): implement @RequirePermission decorator with
SetMetadata+Reflector, register APP_GUARD globally, fix as assertions
to type guards, add explicit return types, fix import type for express,
fix /metrics implicit any, replace native Error with ApplicationError,
remove typeorm remnants, register LifecycleService.

teacher-bff: add logger, ApplicationError, GlobalErrorFilter, forward
real userId to downstream, log downstream failures, migrate health
controller to shared/health.

Go (2 services): interface to any, doc comments, CORS dev whitelist,
JWT secret fail-fast, push-gateway internal API auth, metrics and
readyz endpoints, remove dead code.

Python (2 services): lifespan return type, dev_mode to bool, data-ana
APIRouter, ai POST body model, ClickHouse async wrapping.

services/push-gateway/go.mod

@@ -6,6 +6,7 @@ require (
 	github.com/gin-gonic/gin v1.12.0
 	github.com/golang-jwt/jwt/v5 v5.2.1
 	github.com/gorilla/websocket v1.5.3
+	github.com/prometheus/client_golang v1.23.2
 	go.opentelemetry.io/contrib/instrumentation/github.com/gin-gonic/gin/otelgin v0.69.0
 	go.opentelemetry.io/otel v1.44.0
 	go.opentelemetry.io/otel/exporters/otlp/otlptrace/otlptracehttp v1.44.0
@@ -13,6 +14,7 @@ require (
 )
 
 require (
+	github.com/beorn7/perks v1.0.1 // indirect
 	github.com/bytedance/gopkg v0.1.4 // indirect
 	github.com/bytedance/sonic v1.15.1 // indirect
 	github.com/bytedance/sonic/loader v0.5.1 // indirect
@@ -36,7 +38,11 @@ require (
 	github.com/mattn/go-isatty v0.0.22 // indirect
 	github.com/modern-go/concurrent v0.0.0-20180306012644-bacd9c7ef1dd // indirect
 	github.com/modern-go/reflect2 v1.0.2 // indirect
+	github.com/munnerz/goautoneg v0.0.0-20191010083416-a7dc8b61c822 // indirect
 	github.com/pelletier/go-toml/v2 v2.3.1 // indirect
+	github.com/prometheus/client_model v0.6.2 // indirect
+	github.com/prometheus/common v0.66.1 // indirect
+	github.com/prometheus/procfs v0.16.1 // indirect
 	github.com/quic-go/qpack v0.6.0 // indirect
 	github.com/quic-go/quic-go v0.59.1 // indirect
 	github.com/twitchyliquid64/golang-asm v0.15.1 // indirect
@@ -47,6 +53,7 @@ require (
 	go.opentelemetry.io/otel/metric v1.44.0 // indirect
 	go.opentelemetry.io/otel/trace v1.44.0 // indirect
 	go.opentelemetry.io/proto/otlp v1.10.0 // indirect
+	go.yaml.in/yaml/v2 v2.4.2 // indirect
 	golang.org/x/arch v0.27.0 // indirect
 	golang.org/x/crypto v0.52.0 // indirect
 	golang.org/x/net v0.55.0 // indirect