Refactor server: extract shared helpers, fix tool-call ordering and finish_reason mapping

- Extract callUpstream helper to deduplicate ~30 lines between chatCompletions and responses
- Move HTML templates to internal/server/templates/ via go:embed (server.go 1749→1192 lines)
- Consolidate 4 copies of firstNonEmpty into util.FirstNonEmpty
- Extract chatStreamChunk named type shared by aggregateStream and aggregateResponsesStream
- Fix tool-call ordering: iterate sorted map keys instead of sequential 0..N
- Map upstream finish_reason to Responses API status (length/content_filter → incomplete)
- Surface /v1/models errors as 401/502 instead of silently returning empty 200
- Add Secure cookie flag via isTLSRequest helper
- forEachSSEChunk: use sseDataPayload parser, drop redundant json.Valid, distinguish bufio.ErrTooLong
- Fix StreamIdleTimout typo → StreamIdleTimeout
- sso.go: single Read → io.ReadAll(io.LimitReader), explicit unknown error fallback

internal/config/config.go

@@ -6,6 +6,7 @@ import (
 	"time"
 
 	"git.misaka.ren/M1saka/zhanlu_proxy/internal/auth"
+	"git.misaka.ren/M1saka/zhanlu_proxy/internal/util"
 )
 
 type Config struct {
@@ -25,7 +26,7 @@ type Config struct {
 	LoginPassword      string
 	PluginVersion      string
 	UpstreamTimeout    time.Duration
-	StreamIdleTimout   time.Duration
+	StreamIdleTimeout  time.Duration
 	Debug              bool
 	Credentials        auth.Credentials
 }
@@ -33,7 +34,7 @@ type Config struct {
 func Load() (Config, error) {
 	cfg := Config{
 		ListenAddr:         getenv("ZHANLU_LISTEN_ADDR", ":8080"),
-		MobileLoginBaseURL: firstNonEmpty(os.Getenv("ZHANLU_MOBILE_LOGIN_BASE_URL"), getenv("ZHANLU_SERVER_BASE_URL", "https://ecloud.10086.cn")),
+		MobileLoginBaseURL: util.FirstNonEmpty(os.Getenv("ZHANLU_MOBILE_LOGIN_BASE_URL"), getenv("ZHANLU_SERVER_BASE_URL", "https://ecloud.10086.cn")),
 		MobileModelBaseURL: getenv("ZHANLU_MOBILE_MODEL_BASE_URL", "https://ecloud.10086.cn/api/query/aigateway"),
 		UpstreamPath:       getenv("ZHANLU_UPSTREAM_PATH", "/chat/completions"),
 		DBPath:             getenv("ZHANLU_DB_FILE", "zhanlu.db"),
@@ -48,7 +49,7 @@ func Load() (Config, error) {
 		LoginPassword:      os.Getenv("ZHANLU_LOGIN_PASSWORD"),
 		PluginVersion:      getenv("ZHANLU_PLUGIN_VERSION", "1.4.2"),
 		UpstreamTimeout:    durationEnv("ZHANLU_UPSTREAM_TIMEOUT", 300*time.Second),
-		StreamIdleTimout:   durationEnv("ZHANLU_STREAM_IDLE_TIMEOUT", 300*time.Second),
+		StreamIdleTimeout:  durationEnv("ZHANLU_STREAM_IDLE_TIMEOUT", 300*time.Second),
 		Debug:              strings.EqualFold(os.Getenv("ZHANLU_DEBUG"), "true"),
 	}
 	cfg.Credentials = auth.Credentials{
@@ -81,15 +82,6 @@ func durationEnv(key string, fallback time.Duration) time.Duration {
 	return d
 }
 
-func firstNonEmpty(values ...string) string {
-	for _, v := range values {
-		if strings.TrimSpace(v) != "" {
-			return v
-		}
-	}
-	return ""
-}
-
 const defaultPublicKeyPEM = `-----BEGIN PUBLIC KEY-----
 MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEAhxudxTewPgljUHEZHkusP7m3I+zA4/RGvuUMt6TtII/m4zwUOm/Y31zHBTmkCCt8k5vj9y+AmO0TsGmHooNQuMebakdmEWdcA5h7YAHHFbF2w5LcxIXjib08vgVpA+m3R5xPbLK+vfHe2aAX36b5nHReDNncY5vAl3U4CgIEBGPqyG67vJytRWqP+sfEdw5+m192Rf4SCGyiBzRmjiVlH3zeEBjdbOrkAnzKOVz6AHBl2q7LPLJKIzxjoAyhEp5qnDjHUFo5VZUgFwUOt83A/jbGMyzmjRoxBuvKcs9tBuorZyUwIsZN6E+rtQk2YqMPj4RkDsZ7LRmj6on8sN2rHQIDAQAB
 -----END PUBLIC KEY-----`