chore(compliance): drop opencode zen free-pool from default config and docs

opencode.ai/zen is a free-quota pool for the official opencode app, keyed by
User-Agent fingerprint. Auto-provisioning it in the default config effectively
impersonated the official client to bypass FreeUsageLimitError — a ToS risk.
- default config (Go + GUI embed) now ships NO sources; users add their own
- README/README_EN: remove opencode adapter from built-in list and the zen
  free-pool paragraph
- adapter script and its unit tests stay (explicit opt-in only)

internal/config/config.go

@@ -103,9 +103,10 @@ func EnsureDefault(path string) (bool, error) {
 }
 
 // writeDefaultConfig writes a minimal, safe-by-default config: loopback-only
-// listen, a fresh random admin key, and a no-key zen source that works out of
-// the box. adapter_dir / runtime_file live next to the config file so the
-// binary works regardless of the working directory it is started from.
+// listen and a fresh random admin key. No upstream sources are preconfigured
+// (the repo ships none — add them via WebUI or config.yaml). adapter_dir /
+// runtime_file live next to the config file so the binary works regardless of
+// the working directory it is started from.
 func writeDefaultConfig(path string) error {
 	key, err := NewGatewayKey()
 	if err != nil {
@@ -122,15 +123,6 @@ func writeDefaultConfig(path string) error {
 		DefaultModel: "AUTO",
 		AdapterDir:   filepath.Join(abs, "adapters"),
 		RuntimeFile:  filepath.Join(abs, "runtime.json"),
-		Sources: []Source{
-			{
-				Name:    "zen",
-				BaseURL: "https://opencode.ai/zen/v1",
-				APIKey:  "public", // zen 免费池：官方无 key 客户端实际发送 Bearer public
-				Adapter: "opencode",
-				Models:  []Model{{ID: "deepseek-v4-flash-free", Priority: 100, Kind: "chat"}},
-			},
-		},
 	}
 	out, err := yaml.Marshal(&cfg)
 	if err != nil {