Enforce gofumpt formatter checks in lint workflow

Address review feedback by enforcing formatter checks via golangci-lint fmt --diff in both Makefile lint target and CI lint job.

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_Generated with [`mux`](https://github.com/coder/mux) • Model: `openai:gpt-5.3-codex` • Thinking: `xhigh`_

Author: ThomasK33

.github/workflows/ci.yaml

@@ -36,6 +36,9 @@ jobs:
           version: v2.8
           args: --timeout=5m ./...
 
+      - name: Run golangci-lint formatter checks
+        run: go run github.com/golangci/golangci-lint/v2/cmd/golangci-lint@v2.8.0 fmt --diff
+
       - name: Run govulncheck
         uses: golang/govulncheck-action@b625fbe08f3bccbe446d94fbf87fcc875a4f50ee # v1
         with:

Makefile

@@ -21,6 +21,7 @@ build: $(VENDOR_STAMP)
 lint: $(VENDOR_STAMP)
 	@command -v golangci-lint >/dev/null || (echo "golangci-lint not found; use nix develop" && exit 1)
 	GOFLAGS=$(GOFLAGS) golangci-lint run ./...
+	GOFLAGS=$(GOFLAGS) golangci-lint fmt --diff
 
 vuln: $(VENDOR_STAMP)
 	@command -v govulncheck >/dev/null || (echo "govulncheck not found; use nix develop" && exit 1)