fix(publisher): require the jq and bash it uses; pin CI actions

From the Codex re-gate of the 0.3.3 fixes: NUL-separated discovery
fields need jq 1.7 (--raw-output0) and bash 4.4 (mapfile -d); check both
up front with a clear message instead of failing midway on older tools.
ci.yml actions are pinned to commit SHAs like the release workflows.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01V3syn2fN2LNo5pvTSqc6eh

.github/workflows/ci.yml

@@ -19,13 +19,13 @@ jobs:
 
     steps:
       - name: Checkout
-        uses: actions/checkout@v4
+        uses: actions/checkout@11d5960a326750d5838078e36cf38b85af677262 # v4
 
       - name: Install Nix
-        uses: cachix/install-nix-action@v31
+        uses: cachix/install-nix-action@448cde739abec1eaf0646249e3d25bb8d9bc7702 # v31
 
       - name: Restore and save Nix store
-        uses: nix-community/cache-nix-action@v7
+        uses: nix-community/cache-nix-action@7df957e333c1e5da7721f60227dbba6d06080569 # v7
         with:
           primary-key: nix-v2-${{ runner.os }}-${{ runner.arch }}-${{ hashFiles('flake.nix', 'flake.lock', 'Cargo.lock', 'Cargo.toml') }}-${{ hashFiles('crates/**', 'scripts/**', 'install.sh', 'README.md', 'LICENSE') }}
           restore-prefixes-first-match: |
@@ -47,7 +47,7 @@ jobs:
 
     steps:
       - name: Checkout
-        uses: actions/checkout@v4
+        uses: actions/checkout@11d5960a326750d5838078e36cf38b85af677262 # v4
 
       - name: Test install.sh with sh
         run: scripts/install-sh-test.sh