chore: Enhance backend test coverage and add new functional tests for Security page

- Added tests to `proxyhost_service_validation_test.go` to validate fallback parsing and handle invalid hostname characters.
- Introduced new tests for DNS challenge validation in `proxyhost_service_validation_test.go`.
- Updated `current_spec.md` to reflect changes in testing strategy and coverage goals for PR #729.
- Enhanced `Security.functional.test.tsx` to include navigation test for Notifications button.
- Mocked `useNavigate` from `react-router-dom` to verify navigation behavior in Security page tests.

frontend/src/pages/__tests__/Security.functional.test.tsx

@@ -14,6 +14,16 @@ import * as securityApi from '../../api/security'
 import * as crowdsecApi from '../../api/crowdsec'
 import * as settingsApi from '../../api/settings'
 
+const mockNavigate = vi.hoisted(() => vi.fn())
+
+vi.mock('react-router-dom', async () => {
+  const actual = await vi.importActual<typeof import('react-router-dom')>('react-router-dom')
+  return {
+    ...actual,
+    useNavigate: () => mockNavigate,
+  }
+})
+
 vi.mock('../../api/security')
 vi.mock('../../api/crowdsec')
 vi.mock('../../api/settings')
@@ -168,6 +178,7 @@ describe('Security Page - Functional Tests', () => {
       },
     })
     vi.clearAllMocks()
+    mockNavigate.mockReset()
     vi.mocked(crowdsecApi.statusCrowdsec).mockResolvedValue({ running: false, pid: 0, lapi_ready: false })
     vi.mocked(settingsApi.updateSetting).mockResolvedValue()
   })
@@ -433,6 +444,21 @@ describe('Security Page - Functional Tests', () => {
         expect(screen.getByRole('button', { name: /Notifications/i })).not.toBeDisabled()
       })
     })
+
+    it('should navigate to notifications settings when Notifications button is clicked', async () => {
+      const user = userEvent.setup()
+      vi.mocked(securityApi.getSecurityStatus).mockResolvedValue(mockSecurityStatusAllEnabled)
+
+      await renderSecurityPage()
+
+      await waitFor(() => {
+        expect(screen.getByRole('button', { name: /Notifications/i })).toBeInTheDocument()
+      })
+
+      await user.click(screen.getByRole('button', { name: /Notifications/i }))
+
+      expect(mockNavigate).toHaveBeenCalledWith('/settings/notifications')
+    })
   })
 
   // NOTE: CrowdSec Bouncer Key Display moved to CrowdSecConfig page (Sprint 3)