test: skip keychain unit tests when keychain unavailable

Fixes 4 failing keychain unit tests in Linux CI environment by checking
keychain availability and skipping tests when unavailable.

Modified tests:
- TestEnableKeychain (line 1344)
- TestEnableKeychainAlreadyEnabled (line 1374)
- TestGetKeychainStatus (line 1422)
- TestRemoveVault (line 1458)

Uses KeychainService.IsAvailable() to detect platform support before
running keychain operations.

Generated with Claude Code

Co-Authored-By: Claude <noreply@anthropic.com>

Author: arimxyer

internal/vault/vault_test.go

@@ -1341,6 +1341,11 @@ func TestEnableKeychain(t *testing.T) {
 	vault, _, cleanup := setupTestVault(t)
 	defer cleanup()
 
+	// Skip if keychain is not available (e.g., Linux CI)
+	if !vault.keychainService.IsAvailable() {
+		t.Skip("Keychain not available on this platform")
+	}
+
 	_ = vault.keychainService.Delete()
 	password := "TestPassword123!"
 
@@ -1366,6 +1371,11 @@ func TestEnableKeychainAlreadyEnabled(t *testing.T) {
 	vault, _, cleanup := setupTestVault(t)
 	defer cleanup()
 
+	// Skip if keychain is not available (e.g., Linux CI)
+	if !vault.keychainService.IsAvailable() {
+		t.Skip("Keychain not available on this platform")
+	}
+
 	_ = vault.keychainService.Delete()
 	password := "TestPassword123!"
 
@@ -1409,6 +1419,11 @@ func TestGetKeychainStatus(t *testing.T) {
 	vault, _, cleanup := setupTestVault(t)
 	defer cleanup()
 
+	// Skip if keychain is not available (e.g., Linux CI)
+	if !vault.keychainService.IsAvailable() {
+		t.Skip("Keychain not available on this platform")
+	}
+
 	_ = vault.keychainService.Delete()
 	password := "TestPassword123!"
 
@@ -1440,6 +1455,11 @@ func TestRemoveVault(t *testing.T) {
 	vault, vaultPath, cleanup := setupTestVault(t)
 	defer cleanup()
 
+	// Skip if keychain is not available (e.g., Linux CI)
+	if !vault.keychainService.IsAvailable() {
+		t.Skip("Keychain not available on this platform")
+	}
+
 	_ = vault.keychainService.Delete()
 	password := "TestPassword123!"