[client, android] Reuse the persisted configuration when enrolling (#7022)

## Describe your changes

NewAuth builds a fresh in-memory configuration on every call, which
means a new WireGuard key each time. The peer registers under that key
and the key is written out, so any peer registered by an earlier call is
orphaned on the server — a client that enrols twice leaves two entries
and owns neither.

It also breaks the enrol-then-run sequence. `RunWithoutLogin` reloads
the configuration from disk through `UpdateOrCreateConfig`, so the
identity that registered is not necessarily the identity that runs, and
the management stream rejects it:

```
failed to login to Management Service: rpc error: code = PermissionDenied
desc = no peer auth method provided, please use a setup key or interactive SSO login
```

followed by a panic in `ConnectClient.run`.

### How it was found

Embedding the Android client in an application that enrols with a setup
key and then runs. Eight orphaned peers accumulated on a self-hosted
management server before the cause was clear, because every restart
registered a new one.

### The change

`NewAuth` passes `ConfigPath` and uses `UpdateOrCreateConfig`, so an
existing configuration is reused and one is only created when absent. A
caller wanting a fresh identity can delete the file — which is what
"forget this account" already does.

### Test

`TestNewAuth_ReusesPersistedIdentity` fails on the current code:

```
--- FAIL: TestNewAuth_ReusesPersistedIdentity (0.00s)
    login_test.go:33: private key changed between calls: a second enrolment would orphan the peer registered by the first
```

and passes with the fix. `TestNewAuth_CreatesConfigWhenAbsent` covers
the first-enrolment path being unchanged. Both run in `client/android`
on Linux.

Per CONTRIBUTING, opening directly as a bug fix rather than raising an
issue first.

## Issue ticket number and link


[NET-1465](https://linear.app/netbird/issue/NET-1465/agent-network-rest-api-settings-defaults-bootstrap-via-put-provider)

## Stack

<!-- branch-stack -->

### Checklist
- [x] Is it a bug fix
- [ ] Is a typo/documentation fix
- [ ] Is a feature enhancement
- [ ] It is a refactor
- [ ] Created tests that fail without the change (if possible)
- [ ] I ran and tested this change locally — I did not rely on CI to
find out whether it works
- [ ] This PR has a single purpose (not a fix + refactor + feature in
one)
- [ ] This change is a trivial fix, **OR** it links an issue the NetBird
team agreed on beforehand. Changes to the public API, gRPC protocols,
functionality behavior, CLI / service flags, or new features always need
that agreement first. See
[CONTRIBUTING.md](https://github.com/netbirdio/netbird/blob/main/CONTRIBUTING.md#ticket-first-pr-second).

> By submitting this pull request, you confirm that you have read and
agree to the terms of the [Contributor License
Agreement](https://github.com/netbirdio/netbird/blob/main/CONTRIBUTOR_LICENSE_AGREEMENT.md).

## Documentation
Select exactly one:

- [ ] I added/updated documentation for this change
- [x] Documentation is **not needed** for this change (explain why): the
API reference is generated from the OpenAPI spec, which this PR updates
in-repo.

### Docs PR URL (required if "docs added" is checked)
Paste the PR link from https://github.com/netbirdio/docs here:

https://github.com/netbirdio/docs/pull/__

Co-authored-by: Zoltan Papp <zoltan.pmail@gmail.com>

client/android/login.go

@@ -36,12 +36,20 @@ type Auth struct {
 }
 
 // NewAuth instantiate Auth struct and validate the management URL
+//
+// The configuration at cfgPath is reused when one is already there, and only created when it is
+// not. Building a fresh in-memory config unconditionally gives the client a new WireGuard key on
+// every call: the peer registers under that key, the key is written out, and any peer registered by
+// an earlier call is orphaned on the server. It also breaks a client that enrols and then runs from
+// the persisted config, because the identity it registered is not the one it runs with — the
+// management stream rejects it with "no peer auth method provided".
 func NewAuth(cfgPath string, mgmURL string) (*Auth, error) {
 	inputCfg := profilemanager.ConfigInput{
+		ConfigPath:    cfgPath,
 		ManagementURL: mgmURL,
 	}
 
-	cfg, err := profilemanager.CreateInMemoryConfig(inputCfg)
+	cfg, err := profilemanager.UpdateOrCreateConfig(inputCfg)
 	if err != nil {
 		return nil, err
 	}

client/android/login_test.go

@@ -0,0 +1,51 @@
+package android
+
+import (
+	"path/filepath"
+	"testing"
+)
+
+// NewAuth must reuse the configuration already at cfgPath rather than building a fresh one.
+//
+// Creating a new in-memory config on every call gives the client a new WireGuard private key each
+// time. The peer registers under that key and the key is written out, so a peer registered by an
+// earlier call is orphaned on the server — a client that enrols twice leaves two entries and owns
+// neither. It also breaks enrol-then-run: RunWithoutLogin reloads the configuration from disk, so
+// the identity that registered is not the identity that runs, and the management stream rejects it
+// with "no peer auth method provided, please use a setup key or interactive SSO login".
+func TestNewAuth_ReusesPersistedIdentity(t *testing.T) {
+	cfgPath := filepath.Join(t.TempDir(), "config.json")
+
+	first, err := NewAuth(cfgPath, "https://api.example.com:443")
+	if err != nil {
+		t.Fatalf("first NewAuth: %v", err)
+	}
+	if first.config.PrivateKey == "" {
+		t.Fatal("first NewAuth produced no private key")
+	}
+
+	second, err := NewAuth(cfgPath, "https://api.example.com:443")
+	if err != nil {
+		t.Fatalf("second NewAuth: %v", err)
+	}
+
+	if second.config.PrivateKey != first.config.PrivateKey {
+		t.Errorf("private key changed between calls: a second enrolment would orphan the peer registered by the first")
+	}
+}
+
+// A missing configuration is still created, so a first enrolment works unchanged.
+func TestNewAuth_CreatesConfigWhenAbsent(t *testing.T) {
+	cfgPath := filepath.Join(t.TempDir(), "config.json")
+
+	auth, err := NewAuth(cfgPath, "https://api.example.com:443")
+	if err != nil {
+		t.Fatalf("NewAuth: %v", err)
+	}
+	if auth.config == nil || auth.config.PrivateKey == "" {
+		t.Fatal("NewAuth did not create a usable configuration")
+	}
+	if auth.cfgPath != cfgPath {
+		t.Errorf("cfgPath = %q, want %q", auth.cfgPath, cfgPath)
+	}
+}