feat(entrypoint): add inbound mTLS profiles for HTTPS

Add root-level inbound_mtls_profiles combining optional system CAs with PEM
CA files, and entrypoint.inbound_mtls_profile to require client certificates
on every HTTPS connection. Route-level inbound_mtls_profile is allowed only
without a global profile; per-handshake TLS picks ClientCAs from SNI, and
requests fail with 421 when Host and SNI would select different mTLS routes.

Compile pools at init (SetInboundMTLSProfiles from state.initEntrypoint) and
reject unknown profile refs or mixed global-plus-route configuration.

Extend config.example.yml and package READMEs; add entrypoint and config
tests for TLS mutation, handshakes, and validation.

internal/entrypoint/entrypoint.go

@@ -1,6 +1,7 @@
 package entrypoint
 
 import (
+	"crypto/x509"
 	"net/http"
 	"strings"
 	"sync/atomic"
@@ -41,6 +42,8 @@ type Entrypoint struct {
 	httpPoolDisableLog atomic.Bool
 
 	servers *xsync.Map[string, *httpServer] // listen addr -> server
+
+	inboundMTLSProfiles map[string]*x509.CertPool
 }
 
 var _ entrypoint.Entrypoint = &Entrypoint{}
@@ -62,13 +65,14 @@ func NewEntrypoint(parent task.Parent, cfg *Config) *Entrypoint {
 	}
 
 	ep := &Entrypoint{
-		task:             parent.Subtask("entrypoint", false),
-		cfg:              cfg,
-		findRouteFunc:    findRouteAnyDomain,
-		shortLinkMatcher: newShortLinkMatcher(),
-		streamRoutes:     pool.New[types.StreamRoute]("stream_routes", "stream_routes"),
-		excludedRoutes:   pool.New[types.Route]("excluded_routes", "excluded_routes"),
-		servers:          xsync.NewMap[string, *httpServer](),
+		task:                parent.Subtask("entrypoint", false),
+		cfg:                 cfg,
+		findRouteFunc:       findRouteAnyDomain,
+		shortLinkMatcher:    newShortLinkMatcher(),
+		streamRoutes:        pool.New[types.StreamRoute]("stream_routes", "stream_routes"),
+		excludedRoutes:      pool.New[types.Route]("excluded_routes", "excluded_routes"),
+		servers:             xsync.NewMap[string, *httpServer](),
+		inboundMTLSProfiles: make(map[string]*x509.CertPool),
 	}
 	return ep
 }