fix: handle empty customDomain when checking for isInternalLink (#11609)

This PR improves the portal's internal link detection logic to be more
robust when handling empty or undefined configuration values.
Previously, the code could fail when `customDomain` was empty, causing
external links to incorrectly behave as internal links. The fix
introduces a new `isSameOrigin` helper function that safely compares
URLs using proper URL parsing and origin comparison, gracefully handling
edge cases like missing domains, relative paths, and malformed URLs.
This ensures external links consistently open in new tabs regardless of
portal configuration completeness.

app/javascript/portal/specs/portal.spec.js

@@ -103,7 +103,6 @@ describe('openExternalLinksInNewTab', () => {
     openExternalLinksInNewTab();
 
     const link = simulateClick('#external');
-
     expect(link.target).toBe('_blank');
     expect(link.rel).toBe('noopener noreferrer');
   });
@@ -139,4 +138,48 @@ describe('openExternalLinksInNewTab', () => {
     expect(link.target).toBe('_blank');
     expect(link.rel).toBe('noopener noreferrer');
   });
+
+  it('opens external links in a new tab even if customDomain is empty', () => {
+    window = dom.window;
+    window.portalConfig = {
+      hostURL: 'app.chatwoot.com',
+    };
+
+    global.window = window;
+
+    openExternalLinksInNewTab();
+
+    const link = simulateClick('#external');
+    const internal = simulateClick('#internal');
+    const custom = simulateClick('#custom');
+
+    expect(link.target).toBe('_blank');
+    expect(link.rel).toBe('noopener noreferrer');
+
+    expect(internal.target).not.toBe('_blank');
+    // this will be blank since the configs customDomain is empty
+    // which is a fair expectation
+    expect(custom.target).toBe('_blank');
+  });
+
+  it('opens external links in a new tab even if hostURL is empty', () => {
+    window = dom.window;
+    window.portalConfig = {
+      customDomain: 'custom.domain.com',
+    };
+
+    global.window = window;
+
+    openExternalLinksInNewTab();
+
+    const link = simulateClick('#external');
+    const internal = simulateClick('#internal');
+    const custom = simulateClick('#custom');
+
+    expect(link.target).toBe('_blank');
+    expect(link.rel).toBe('noopener noreferrer');
+
+    expect(internal.target).not.toBe('_blank');
+    expect(custom.target).not.toBe('_blank');
+  });
 });