fix: harden GitHub Actions workflows (zizmor) (#44)

- Upgrade actions/checkout from v4 to v6.0.2 (SHA-pinned) across all workflows
- Add persist-credentials: false to all checkout steps that don't need
  git credentials (all CI jobs, and release build/publish jobs)
- Fix excessive-permissions in release.yml: replace workflow-level
  contents:write + id-token:write with permissions:{} at workflow level
  and minimal per-job permissions (contents:write only for sync-and-tag
  and github-release; contents:read + id-token:write for publish jobs)

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: reberhardt7

.github/workflows/ci.yml

@@ -13,7 +13,9 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout
-        uses: actions/checkout@34e114876b0b11c390a56381ad16ebd13914f8d5 # v4
+        uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
+        with:
+          persist-credentials: false
 
       - name: Install Rust
         uses: dtolnay/rust-toolchain@efa25f7f19611383d5b0ccf2d1c8914531636bf9 # stable
@@ -41,7 +43,9 @@ jobs:
     runs-on: ${{ matrix.os }}
     steps:
       - name: Checkout
-        uses: actions/checkout@34e114876b0b11c390a56381ad16ebd13914f8d5 # v4
+        uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
+        with:
+          persist-credentials: false
 
       - name: Install Rust
         uses: dtolnay/rust-toolchain@efa25f7f19611383d5b0ccf2d1c8914531636bf9 # stable
@@ -65,7 +69,9 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout
-        uses: actions/checkout@34e114876b0b11c390a56381ad16ebd13914f8d5 # v4
+        uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
+        with:
+          persist-credentials: false
 
       - name: Setup Node.js
         uses: actions/setup-node@49933ea5288caeca8642d1e84afbd3f7d6820020 # v4
@@ -112,7 +118,9 @@ jobs:
     runs-on: ${{ matrix.os }}
     steps:
       - name: Checkout
-        uses: actions/checkout@34e114876b0b11c390a56381ad16ebd13914f8d5 # v4
+        uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
+        with:
+          persist-credentials: false
 
       - name: Install Rust
         uses: dtolnay/rust-toolchain@efa25f7f19611383d5b0ccf2d1c8914531636bf9 # stable

.github/workflows/release.yml

@@ -13,18 +13,18 @@ on:
           - minor
           - major
 
-permissions:
-  contents: write
-  id-token: write
+permissions: {}
 
 jobs:
   sync-and-tag:
     runs-on: ubuntu-latest
+    permissions:
+      contents: write
     outputs:
       version: ${{ steps.sync.outputs.VERSION }}
     steps:
       - name: Checkout
-        uses: actions/checkout@34e114876b0b11c390a56381ad16ebd13914f8d5 # v4
+        uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
 
       - name: Configure Git
         run: |
@@ -117,11 +117,14 @@ jobs:
             archive: tar.gz
             build-tool: cross
     runs-on: ${{ matrix.runner }}
+    permissions:
+      contents: read
     steps:
       - name: Checkout
-        uses: actions/checkout@34e114876b0b11c390a56381ad16ebd13914f8d5 # v4
+        uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
         with:
           ref: v${{ needs.sync-and-tag.outputs.version }}
+          persist-credentials: false
 
       - name: Install Rust
         uses: dtolnay/rust-toolchain@efa25f7f19611383d5b0ccf2d1c8914531636bf9 # stable
@@ -171,6 +174,8 @@ jobs:
   github-release:
     needs: [sync-and-tag, build]
     runs-on: ubuntu-latest
+    permissions:
+      contents: write
     steps:
       - name: Download all artifacts
         uses: actions/download-artifact@d3f86a106a0bac45b974a628896c90dbdf5c8093 # v4
@@ -196,9 +201,10 @@ jobs:
       id-token: write
     steps:
       - name: Checkout
-        uses: actions/checkout@34e114876b0b11c390a56381ad16ebd13914f8d5 # v4
+        uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
         with:
           ref: v${{ needs.sync-and-tag.outputs.version }}
+          persist-credentials: false
 
       - name: Install Rust
         uses: dtolnay/rust-toolchain@efa25f7f19611383d5b0ccf2d1c8914531636bf9 # stable
@@ -233,9 +239,10 @@ jobs:
       id-token: write
     steps:
       - name: Checkout
-        uses: actions/checkout@34e114876b0b11c390a56381ad16ebd13914f8d5 # v4
+        uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
         with:
           ref: v${{ needs.sync-and-tag.outputs.version }}
+          persist-credentials: false
 
       - name: Configure git for HTTPS
         run: git config --global url."https://github.com/".insteadOf "ssh://git@github.com/"
@@ -308,9 +315,10 @@ jobs:
       id-token: write
     steps:
       - name: Checkout
-        uses: actions/checkout@34e114876b0b11c390a56381ad16ebd13914f8d5 # v4
+        uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
         with:
           ref: v${{ needs.sync-and-tag.outputs.version }}
+          persist-credentials: false
 
       - name: Download all artifacts
         uses: actions/download-artifact@d3f86a106a0bac45b974a628896c90dbdf5c8093 # v4