feat: 密钥静态加密 + /api/v1 agent 管理 API

密钥加密（写侧封存 / 读侧解封）
- config.yaml 的 sources[].api_key、sources[].headers、keys[].key 落盘即
  AES-256-GCM 密文（enc:v1: 前缀），master.key 复用 runtime store 那把
- 内存里永远是明文：鉴权比对、API 返回新建 key、WebUI 编辑回填都不受影响
- 启动时一次性封存现存明文（幂等，已封存则不写盘）；-check 不写文件
- UpsertSourceInYAML 增加 box 参数，新加的源不再以明文落盘
- 解密失败改为硬错误：原先 MustDecrypt 返回密文会被下次 Save 二次封存
  （实测：源 key 18→20、静默损坏），现在启动即失败且配置分毫不动

/api/v1：面向 agent 的管理 API（WebUI 零影响）
- GET /api/v1            机器可读索引，列出每个端点的方法/权限/用途
- GET /api/v1/overview   一次调用看全貌：源 + AUTO 链 + 密钥数 + 健康度
- GET /api/v1/health     仅健康快照
- GET /api/v1/models     按源分组的可路由模型清单
- GET /api/v1/sources[/{name}]  凭据遮蔽后的源
- GET /api/v1/auto       调度链与实时槽位状态
- GET /api/v1/keys       admin only，密钥元数据，绝不回显密钥本身
- 沿用同一套网关 key 鉴权；读端点任意角色，写仍需 admin

测试：15 个新用例（含负向：泄密、越权、写操作必须被拒）
变异验证：maskKey 不遮蔽→红、去掉 admin 校验→红

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

internal/core/core.go

@@ -7,6 +7,7 @@ import (
 	"crypto/rand"
 	"encoding/hex"
 	"fmt"
+	"log"
 	"os"
 	"path/filepath"
 	"sort"
@@ -53,6 +54,10 @@ func NewFromConfig(cfg *config.Config) (*Core, error) {
 		return nil, fmt.Errorf("lua vm: %w", err)
 	}
 	c.store = config.NewStore(cfg.RuntimeFile)
+	// Share one box between the runtime store and config.yaml so a single
+	// master.key seals both files. config.Load left the config holding
+	// ciphertext (if it was sealed); unseal it now that the box exists.
+	cfg.AttachSecretBox(c.store.SecretBox())
 	if err := c.store.Load(); err != nil {
 		return nil, fmt.Errorf("runtime store: %w", err)
 	}
@@ -74,6 +79,12 @@ func NewFromConfig(cfg *config.Config) (*Core, error) {
 	if err := c.seedPresetTemplates(); err != nil {
 		return nil, fmt.Errorf("seed preset templates: %w", err)
 	}
+	// Seal any credential still in the clear in config.yaml. Idempotent: an
+	// already-sealed config is not rewritten, so a normal restart writes
+	// nothing. This is the only place that rewrites the file on startup.
+	if err := cfg.NormalizeSecretsForRun(c.store.SecretBox()); err != nil {
+		return nil, fmt.Errorf("normalize secrets: %w", err)
+	}
 	return c, nil
 }
 
@@ -439,6 +450,11 @@ func (c *Core) mergedSources() []config.Source {
 }
 
 // resolveSourceKey applies api_key_env and decrypts enc:v1: ciphertext.
+// Config values are already unsealed at startup (Config.NormalizeSecretsForRun),
+// so the decrypt branch is the belt-and-braces path for a source that arrived
+// already sealed through another route. A failure there leaves the ciphertext in
+// place, which makes the upstream reject the key loudly rather than sending an
+// empty Authorization header that might look like a config-less source.
 func (c *Core) resolveSourceKey(s config.Source) config.Source {
 	if s.APIKeyEnv != "" {
 		if v := os.Getenv(s.APIKeyEnv); v != "" {
@@ -447,7 +463,11 @@ func (c *Core) resolveSourceKey(s config.Source) config.Source {
 		return s
 	}
 	if box := c.store.SecretBox(); box != nil && strings.HasPrefix(s.APIKey, "enc:v1:") {
-		s.APIKey = box.MustDecrypt(s.APIKey)
+		if v, err := box.Decrypt(s.APIKey); err == nil {
+			s.APIKey = v
+		} else {
+			log.Printf("[core] source %s: api_key decrypt failed: %v", s.Name, err)
+		}
 	}
 	return s
 }
@@ -655,7 +675,7 @@ func (c *Core) AddSource(src config.Source) error {
 	if err := normalizeSource(&src); err != nil {
 		return err
 	}
-	if err := config.UpsertSourceInYAML(c.cfg.Path, src.Name, src); err != nil {
+	if err := config.UpsertSourceInYAML(c.cfg.Path, src.Name, src, c.cfg.SecretBox()); err != nil {
 		return err
 	}
 	// Update in-memory Sources so mergedSources() finds the entry.