fix: resolve all golangci-lint issues

Fixes #32

Changes:
- middleware.go: use max() builtin, strconv.Itoa, fix wsl whitespace
- database.go: fix nlreturn, noinlineerr, wsl whitespace
- handlers.go: remove unnecessary template.HTML conversion, unused import
- app.go: extract cleanupContainer to fix nestif, fix lll
- client.go: break long string literals to fix lll
- deploy.go: fix wsl whitespace
- auth_test.go: extract helpers to fix funlen, fix wsl/nlreturn/testifylint
- handlers_test.go: deduplicate IDOR tests, fix paralleltest
- validation_test.go: add parallel, fix funlen/wsl, nolint testpackage
- port_validation_test.go: add parallel, nolint testpackage
- ratelimit_test.go: add parallel where safe, nolint testpackage/paralleltest
- realip_test.go: add parallel, use NewRequestWithContext, fix wsl/funlen
- user.go: (noinlineerr already fixed by database.go pattern)

internal/middleware/middleware.go

@@ -2,11 +2,11 @@
 package middleware
 
 import (
-	"fmt"
 	"log/slog"
 	"math"
 	"net"
 	"net/http"
+	"strconv"
 	"strings"
 	"sync"
 	"time"
@@ -225,6 +225,7 @@ func (i *ipLimiter) sweep(now time.Time) {
 			delete(i.limiters, ip)
 		}
 	}
+
 	i.lastSweep = now
 }
 
@@ -246,6 +247,7 @@ func (i *ipLimiter) getLimiter(ip string) *rate.Limiter {
 		}
 		i.limiters[ip] = entry
 	}
+
 	entry.lastSeen = now
 
 	return entry.limiter
@@ -276,11 +278,9 @@ func (m *Middleware) LoginRateLimit() func(http.Handler) http.Handler {
 				reservation := limiter.Reserve()
 				delay := reservation.Delay()
 				reservation.Cancel()
-				retryAfter := int(math.Ceil(delay.Seconds()))
-				if retryAfter < 1 {
-					retryAfter = 1
-				}
-				writer.Header().Set("Retry-After", fmt.Sprintf("%d", retryAfter))
+
+				retryAfter := max(int(math.Ceil(delay.Seconds())), 1)
+				writer.Header().Set("Retry-After", strconv.Itoa(retryAfter))
 
 				http.Error(
 					writer,