feat(vault-tui): implement KV client and service for managing secrets

- Added internal/vault/client.go for creating a Vault client with configuration settings.
- Introduced internal/vault/errors.go to classify Vault API errors for better UI handling.
- Created internal/vault/kv.go to manage KV secrets, including listing, reading, writing, and deleting operations.
- Implemented internal/vault/mounts.go to list and describe secret engine mounts.
- Developed internal/vault/service.go to provide a unified entry point for Vault operations.
- Added internal/vault/kv_test.go for comprehensive testing of KV operations.
- Introduced internal/ui/toast.go for transient notifications in the UI.
- Added renovate.json for dependency management and updates.

internal/auth/m_github.go

@@ -0,0 +1,29 @@
+package auth
+
+import (
+	"context"
+
+	"github.com/hashicorp/vault/api"
+)
+
+func init() { register(githubMethod{}) }
+
+type githubMethod struct{}
+
+func (githubMethod) Name() string         { return "github" }
+func (githubMethod) DisplayName() string  { return "GitHub" }
+func (githubMethod) DefaultMount() string { return "github" }
+
+func (githubMethod) Fields() []Field {
+	return []Field{
+		{Name: "token", Label: "GitHub personal access token", Kind: FieldSecret, Required: true,
+			EnvFallback: []string{"VAULT_AUTH_GITHUB_TOKEN"}},
+	}
+}
+
+func (githubMethod) Login(ctx context.Context, c *api.Client, req Request) (*api.Secret, error) {
+	mount := mountOf(req, "github")
+	return loginWrite(ctx, c, mount, "login", map[string]interface{}{
+		"token": req.Creds.Get("token"),
+	})
+}