fix: upgrade security-sensitive Go dependencies

Require Go 1.26.5, gRPC 1.82.1, and x/text 0.39.0 while retaining the dependency graph's existing pins wherever MVS permits. Restore the blocking govulncheck job and correct the documented security advisories.

.github/workflows/vulncheck.yml

@@ -0,0 +1,36 @@
+name: VulnCheck
+
+on:
+  pull_request:
+    branches:
+      - master
+  push:
+    branches:
+      - master
+  workflow_dispatch:
+
+permissions:
+  contents: read
+
+jobs:
+  vulncheck:
+    name: Analysis
+    runs-on: ubuntu-latest
+    timeout-minutes: 20
+    steps:
+      - name: Check out code
+        uses: actions/checkout@v4
+
+      - name: Set up Go
+        uses: actions/setup-go@v5
+        with:
+          go-version-file: go.mod
+          cache: true
+
+      - name: Install govulncheck
+        run: |
+          go install golang.org/x/vuln/cmd/govulncheck@v1.6.0
+          echo "$(go env GOPATH)/bin" >> "${GITHUB_PATH}"
+
+      - name: Run govulncheck
+        run: govulncheck -show verbose ./...