feat: add AI code reviewer using Gemini API

.github/workflows/ai-review.yml

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+name: AI Code Reviewer
+
+on:
+  pull_request:
+    types: [opened, synchronize]
+
+permissions:
+  pull-requests: write
+  contents: read
+
+jobs:
+  review:
+    name: Gemini AI Review
+    runs-on: ubuntu-latest
+    timeout-minutes: 5
+    steps:
+      - uses: actions/checkout@v4
+        with:
+          fetch-depth: 0
+
+      - uses: oven-sh/setup-bun@v2
+        with:
+          bun-version: latest
+
+      - name: Run AI Review
+        env:
+          # Use user's PAT to count towards their GitHub contribution graph, fallback to standard bot token
+          GITHUB_TOKEN: ${{ secrets.GH_PAT || secrets.GITHUB_TOKEN }}
+          GEMINI_API_KEY: ${{ secrets.GEMINIKEY }}
+          PR_NUMBER: ${{ github.event.pull_request.number }}
+          REPO: ${{ github.repository }}
+          BASE_SHA: ${{ github.event.pull_request.base.sha }}
+          HEAD_SHA: ${{ github.event.pull_request.head.sha }}
+        run: bun run scripts/ai-review.ts

scripts/ai-review.ts

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+import { execSync } from 'child_process';
+
+const GEMINI_API_KEY = process.env.GEMINI_API_KEY;
+const GITHUB_TOKEN = process.env.GITHUB_TOKEN;
+const PR_NUMBER = process.env.PR_NUMBER;
+const REPO = process.env.REPO;
+const BASE_SHA = process.env.BASE_SHA;
+const HEAD_SHA = process.env.HEAD_SHA;
+
+if (!GEMINI_API_KEY) {
+  console.log("GEMINI_API_KEY is not set. Skipping AI review.");
+  process.exit(0);
+}
+
+if (!GITHUB_TOKEN) {
+  console.log("GITHUB_TOKEN is not set. Skipping AI review.");
+  process.exit(0);
+}
+
+async function run() {
+  try {
+    // 1. Get the diff
+    console.log(`Getting diff between ${BASE_SHA} and ${HEAD_SHA}`);
+    const diff = execSync(`git diff ${BASE_SHA} ${HEAD_SHA}`).toString();
+
+    if (!diff.trim()) {
+      console.log("No diff found. Skipping review.");
+      return;
+    }
+
+    if (diff.length > 50000) {
+      console.log("Diff is too large for AI review (max 50,000 characters). Skipping.");
+      return;
+    }
+
+    // 2. Call Gemini API
+    console.log("Requesting review from Gemini 1.5 Flash...");
+    const prompt = `You are a senior software engineer conducting a code review on a pull request.
+Review the following git diff and provide constructive, human-like, and professional feedback.
+Focus on identifying logic errors, security issues, performance bottlenecks, and best practice violations.
+If the code looks perfect, say so in a friendly way.
+
+Important constraints:
+- Do NOT output any internal reasoning, thoughts, or <think> tags.
+- Output ONLY the final review in markdown format.
+- Be concise but thorough.
+
+Diff:
+\`\`\`diff
+${diff}
+\`\`\`
+`;
+
+    // We use the same API endpoint format from your curl command
+    const response = await fetch(`https://generativelanguage.googleapis.com/v1beta/models/gemini-1.5-flash-latest:generateContent?key=${GEMINI_API_KEY}`, {
+      method: 'POST',
+      headers: {
+        'Content-Type': 'application/json'
+      },
+      body: JSON.stringify({
+        contents: [
+          {
+            parts: [
+              {
+                text: prompt
+              }
+            ]
+          }
+        ]
+      })
+    });
+
+    if (!response.ok) {
+      const errorText = await response.text();
+      console.error(`Gemini API Error: ${response.status} - ${errorText}`);
+      process.exit(1);
+    }
+
+    const data = await response.json();
+    let reviewComment = data.candidates?.[0]?.content?.parts?.[0]?.text;
+
+    if (!reviewComment) {
+      console.error("No content received from Gemini.");
+      process.exit(1);
+    }
+
+    // Add a signature
+    reviewComment += "\n\n— *AI Code Review (Powered by Gemini)*";
+
+    // 3. Post to GitHub
+    console.log("Posting review to GitHub PR...");
+    const ghResponse = await fetch(`https://api.github.com/repos/${REPO}/pulls/${PR_NUMBER}/reviews`, {
+      method: 'POST',
+      headers: {
+        'Authorization': `Bearer ${GITHUB_TOKEN}`,
+        'Accept': 'application/vnd.github.v3+json',
+        'X-GitHub-Api-Version': '2022-11-28'
+      },
+      body: JSON.stringify({
+        body: reviewComment,
+        event: 'COMMENT'
+      })
+    });
+
+    if (!ghResponse.ok) {
+      const ghError = await ghResponse.text();
+      console.error(`GitHub API Error: ${ghResponse.status} - ${ghError}`);
+      process.exit(1);
+    }
+
+    console.log("Review successfully posted!");
+
+  } catch (error) {
+    console.error("Error during AI review:", error);
+    process.exit(1);
+  }
+}
+
+run();