chore: remediate 61 Go linting issues and tighten pre-commit config

Complete lint remediation addressing errcheck, gosec, and staticcheck
violations across backend test files. Tighten pre-commit configuration
to prevent future blind spots.

Key Changes:
- Fix 61 Go linting issues (errcheck, gosec G115/G301/G304/G306, bodyclose)
- Add proper error handling for json.Unmarshal, os.Setenv, db.Close(), w.Write()
- Fix gosec G115 integer overflow with strconv.FormatUint
- Add #nosec annotations with justifications for test fixtures
- Fix SecurityService goroutine leaks (add Close() calls)
- Fix CrowdSec tar.gz non-deterministic ordering with sorted keys

Pre-commit Hardening:
- Remove test file exclusion from golangci-lint hook
- Add gosec to .golangci-fast.yml with critical checks (G101, G110, G305)
- Replace broad .golangci.yml exclusions with targeted path-specific rules
- Test files now linted on every commit

Test Fixes:
- Fix emergency route count assertions (1→2 for dual-port setup)
- Fix DNS provider service tests with proper mock setup
- Fix certificate service tests with deterministic behavior

Backend: 27 packages pass, 83.5% coverage
Frontend: 0 lint warnings, 0 TypeScript errors
Pre-commit: All 14 hooks pass (~37s)

frontend/src/components/__tests__/DNSProviderForm.test.tsx

@@ -4,6 +4,7 @@ import userEvent from '@testing-library/user-event'
 import { QueryClient, QueryClientProvider } from '@tanstack/react-query'
 import DNSProviderForm from '../DNSProviderForm'
 import { defaultProviderSchemas } from '../../data/dnsProviderSchemas'
+import type { DNSProvider } from '../../api/dnsProviders'
 
 // Mock hooks used by DNSProviderForm
 vi.mock('../../hooks/useDNSProviders', () => ({
@@ -47,7 +48,7 @@ describe('DNSProviderForm — Script provider (accessibility)', () => {
   })
 
   it('renders Script Path when editing an existing script provider (not required)', async () => {
-    const existingProvider = {
+    const existingProvider: DNSProvider = {
       id: 1,
       uuid: 'p-1',
       name: 'local-script',
@@ -64,7 +65,7 @@ describe('DNSProviderForm — Script provider (accessibility)', () => {
     }
 
     renderWithClient(
-      <DNSProviderForm open={true} onOpenChange={() => {}} provider={existingProvider as any} onSuccess={() => {}} />
+      <DNSProviderForm open={true} onOpenChange={() => {}} provider={existingProvider} onSuccess={() => {}} />
     )
 
     // Since provider prop is provided, providerType should be pre-populated and the field rendered