Add trusted publishing workflow and pin action refs

- Add push_gem.yml for RubyGems trusted publishing on v* tags
- Add dependabot.yml for automated GitHub Actions updates
- Pin all action refs to commit SHAs in ci.yml and push_gem.yml

Author: knu

.github/dependabot.yml

@@ -0,0 +1,10 @@
+version: 2
+updates:
+  - package-ecosystem: "github-actions"
+    directory: "/"
+    schedule:
+      interval: "weekly"
+    groups:
+      github-actions:
+        patterns:
+          - "*"

.github/workflows/ci.yml

@@ -25,10 +25,10 @@ jobs:
           - "3.4"
           - ruby
     steps:
-      - uses: actions/checkout@v6
+      - uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd  # v6.0.2
 
       - name: Set up Ruby
-        uses: ruby/setup-ruby@v1
+        uses: ruby/setup-ruby@3ff19f5e2baf30647122352b96108b1fbe250c64  # v1.299.0
         with:
           ruby-version: ${{ matrix.ruby }}
           bundler-cache: true

.github/workflows/push_gem.yml

@@ -0,0 +1,45 @@
+name: Publish gem to rubygems.org
+
+on:
+  push:
+    tags:
+      - "v*"
+
+permissions:
+  contents: read
+
+jobs:
+  push:
+    if: github.repository == "huginn/huginn_agent"
+    runs-on: ubuntu-latest
+
+    environment:
+      name: rubygems.org
+      url: https://rubygems.org/gems/huginn_agent
+
+    permissions:
+      contents: write
+      id-token: write
+
+    steps:
+      - name: Harden Runner
+        uses: step-security/harden-runner@fe104658747b27e96e4f7e80cd0a94068e53901d  # v2.16.1
+        with:
+          egress-policy: audit
+
+      - uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd  # v6.0.2
+
+      - name: Set up Ruby
+        uses: ruby/setup-ruby@3ff19f5e2baf30647122352b96108b1fbe250c64  # v1.299.0
+        with:
+          ruby-version: ruby
+
+      - name: Publish to RubyGems
+        uses: rubygems/release-gem@6317d8d1f7e28c24d28f6eff169ea854948bd9f7  # v1.2.0
+
+      - name: Create GitHub release
+        run: |
+          tag_name="$(git describe --tags --abbrev=0)"
+          gh release create "${tag_name}" --verify-tag --generate-notes
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}