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/ImportSitesModal.test.tsx

@@ -1,11 +1,12 @@
 import { render, screen, fireEvent, waitFor } from '@testing-library/react'
 import ImportSitesModal from './ImportSitesModal'
 import { vi } from 'vitest'
+import { CaddyFile } from '../api/import'
 
 // Mock the upload API used by the component
 const mockUpload = vi.fn()
 vi.mock('../api/import', () => ({
-  uploadCaddyfilesMulti: (...args: unknown[]) => mockUpload(...(args as any[])),
+  uploadCaddyfilesMulti: (files: CaddyFile[]) => mockUpload(files),
 }))
 
 describe('ImportSitesModal', () => {