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/docker/client.go

@@ -611,10 +611,13 @@ func (c *Client) createGitContainer(
 	var script string
 	if cfg.commitSHA != "" {
 		// Clone without depth limit so we can checkout any commit, then checkout specific SHA
-		script = `git clone --branch "$CLONE_BRANCH" "$CLONE_URL" /repo && cd /repo && git checkout "$CLONE_SHA" && echo COMMIT:$(git rev-parse HEAD)`
+		script = `git clone --branch "$CLONE_BRANCH" "$CLONE_URL" /repo` +
+			` && cd /repo && git checkout "$CLONE_SHA"` +
+			` && echo COMMIT:$(git rev-parse HEAD)`
 	} else {
 		// Shallow clone of branch HEAD, then output commit SHA
-		script = `git clone --depth 1 --branch "$CLONE_BRANCH" "$CLONE_URL" /repo && cd /repo && echo COMMIT:$(git rev-parse HEAD)`
+		script = `git clone --depth 1 --branch "$CLONE_BRANCH" "$CLONE_URL" /repo` +
+			` && cd /repo && echo COMMIT:$(git rev-parse HEAD)`
 	}
 
 	env := []string{