chore: add GitHub Actions workflows for community management (#2022)

- Add AI Moderator workflow for spam and AI content detection
- Add Welcome New Contributors workflow for first-time contributors
- Configure necessary permissions and triggers for both workflows

Author: wang1212

.github/workflows/moderator.yml

@@ -0,0 +1,30 @@
+name: AI Moderator
+on:
+  issues:
+    types: [opened]
+  issue_comment:
+    types: [created]
+  pull_request_review_comment:
+    types: [created]
+
+jobs:
+  spam-detection:
+    runs-on: ubuntu-latest
+    permissions:
+      issues: write
+      pull-requests: write
+      models: read
+      contents: read
+    steps:
+      - uses: actions/checkout@v4
+      - uses: github/ai-moderator@v1
+        with:
+          token: ${{ secrets.GITHUB_TOKEN }}
+          spam-label: 'spam'
+          ai-label: 'ai-generated'
+          minimize-detected-comments: true
+          # Built-in prompt configuration (all enabled by default)
+          enable-spam-detection: true
+          enable-link-spam-detection: true
+          enable-ai-detection: true
+          # custom-prompt-path: '.github/prompts/my-custom.prompt.yml'  # Optional

.github/workflows/welcome-new-contributors.yml

@@ -0,0 +1,40 @@
+name: Welcome New Contributors
+
+on:
+  pull_request:
+    types: [opened]
+
+permissions:
+  pull-requests: write
+  models: read
+
+jobs:
+  welcome:
+    runs-on: ubuntu-latest
+    if: github.event.pull_request.author_association == 'FIRST_TIME_CONTRIBUTOR'
+    steps:
+      - name: Generate welcome message
+        uses: actions/ai-inference@v1
+        id: ai
+        with:
+          prompt: |
+            Write a friendly welcome message for a first-time contributor. Include:
+            1. Thank them for their first PR
+            2. Mention checking CONTRIBUTING.md
+            3. Offer to help if they have questions
+
+            Keep it brief and encouraging.
+          model: openai/gpt-4o-mini
+          temperature: 0.7
+
+      - name: Post welcome comment
+        uses: actions/github-script@v7
+        with:
+          script: |
+            const message = `${{ steps.ai.outputs.response }}`;
+            await github.rest.issues.createComment({
+              owner: context.repo.owner,
+              repo: context.repo.repo,
+              issue_number: ${{ github.event.pull_request.number }},
+              body: message
+            });