Add and configure Capslock

Add Capslock (<https://github.com/google/capslock>) as a tool dependency
and use it to continuously check (statically) the capabilities used by
dependencies. The idea behind doing this is to ensure all potentially
dangerous function being used are known and make sense in the context in
which they're used.

The `capabilities.json` file is included in the commit history because
it is needed to do a comparison from one version to the next.

.github/workflows/audit.yml

@@ -4,6 +4,7 @@ on:
     paths:
     - '**/*.go'
     - .github/workflows/audit.yml
+    - capabilities.json
     - go.mod
     - go.sum
   push:
@@ -16,6 +17,25 @@ on:
 permissions: read-all
 
 jobs:
+  capabilities:
+    name: Capabilities
+    runs-on: ubuntu-24.04
+    steps:
+    - name: Checkout repository
+      uses: actions/checkout@v4.2.0
+    - name: Install Go
+      uses: actions/setup-go@v5.0.2
+      with:
+        go-version-file: go.mod
+    - name: Verify action checksums
+      env:
+        JOB: ${{ github.job }}
+        WORKFLOW: ${{ github.workflow_ref }}
+      run: |
+        WORKFLOW=$(echo "$WORKFLOW" | cut -d '@' -f 1 | cut -d '/' -f 3-5)
+        go run ./cmd/ghasum verify -cache /home/runner/work/_actions -no-evict -offline "$WORKFLOW:$JOB"
+    - name: Audit
+      run: go run tasks.go audit-capabilities
   vulnerabilities:
     name: Vulnerabilities
     runs-on: ubuntu-24.04
@@ -34,4 +54,4 @@ jobs:
         WORKFLOW=$(echo "$WORKFLOW" | cut -d '@' -f 1 | cut -d '/' -f 3-5)
         go run ./cmd/ghasum verify -cache /home/runner/work/_actions -no-evict -offline "$WORKFLOW:$JOB"
     - name: Audit
-      run: go run tasks.go audit
+      run: go run tasks.go audit-vulnerabilities