ci: Add companion agent release workflow

Production build pipeline for companion agent:

- Triggers on version tags (v*.*.*)
- Cross-compiles for Linux and Windows (AMD64)
- Generates SHA256 checksums for verification
- Creates Gitea release with auto-generated notes
- Uploads binaries and checksums as release assets
- Provides build summary in workflow output

Built artifacts:
- corrosion-companion-linux-amd64
- corrosion-companion-windows-amd64.exe
- checksums.txt

Usage: git tag v1.0.0 && git push origin v1.0.0

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

.gitea/workflows/build-companion.yml

@@ -0,0 +1,126 @@
+name: Build Companion Agent
+
+on:
+  push:
+    tags:
+      - 'v*.*.*'  # Trigger on version tags (v1.0.0, v1.2.3, etc.)
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v4
+
+      - name: Set up Go
+        uses: actions/setup-go@v4
+        with:
+          go-version: '1.21'
+
+      - name: Get version from tag
+        id: version
+        run: echo "VERSION=${GITHUB_REF#refs/tags/}" >> $GITHUB_OUTPUT
+
+      - name: Build Linux AMD64
+        run: |
+          cd companion-agent
+          mkdir -p bin
+          GOOS=linux GOARCH=amd64 go build -ldflags "-s -w" -o bin/corrosion-companion-linux-amd64 ./cmd/agent
+          chmod +x bin/corrosion-companion-linux-amd64
+
+      - name: Build Windows AMD64
+        run: |
+          cd companion-agent
+          GOOS=windows GOARCH=amd64 go build -ldflags "-s -w" -o bin/corrosion-companion-windows-amd64.exe ./cmd/agent
+
+      - name: Generate checksums
+        run: |
+          cd companion-agent/bin
+          sha256sum corrosion-companion-linux-amd64 > checksums.txt
+          sha256sum corrosion-companion-windows-amd64.exe >> checksums.txt
+          cat checksums.txt
+
+      - name: Create Release
+        uses: actions/github-script@v6
+        env:
+          VERSION: ${{ steps.version.outputs.VERSION }}
+        with:
+          script: |
+            const fs = require('fs').promises;
+            const path = require('path');
+
+            // Create release
+            const release = await github.rest.repos.createRelease({
+              owner: context.repo.owner,
+              repo: context.repo.repo,
+              tag_name: process.env.VERSION,
+              name: `Companion Agent ${process.env.VERSION}`,
+              body: `## Corrosion Companion Agent ${process.env.VERSION}
+
+            ### Installation
+
+            **Linux:**
+            \`\`\`bash
+            wget https://git.corrosionmgmt.com/vantzs/corrosion-admin-panel/releases/download/${process.env.VERSION}/corrosion-companion-linux-amd64
+            chmod +x corrosion-companion-linux-amd64
+            sudo mv corrosion-companion-linux-amd64 /usr/local/bin/corrosion-companion
+            \`\`\`
+
+            **Windows:**
+            Download \`corrosion-companion-windows-amd64.exe\` and run as administrator.
+
+            ### Checksums
+            See \`checksums.txt\` for SHA256 verification.
+
+            ### What's New
+            - Built from commit: ${context.sha.substring(0, 7)}
+            - Go version: 1.21
+            - Platforms: Linux AMD64, Windows AMD64
+            `,
+              draft: false,
+              prerelease: false
+            });
+
+            console.log(`Created release: ${release.data.html_url}`);
+
+            // Upload Linux binary
+            await github.rest.repos.uploadReleaseAsset({
+              owner: context.repo.owner,
+              repo: context.repo.repo,
+              release_id: release.data.id,
+              name: 'corrosion-companion-linux-amd64',
+              data: await fs.readFile('companion-agent/bin/corrosion-companion-linux-amd64')
+            });
+
+            // Upload Windows binary
+            await github.rest.repos.uploadReleaseAsset({
+              owner: context.repo.owner,
+              repo: context.repo.repo,
+              release_id: release.data.id,
+              name: 'corrosion-companion-windows-amd64.exe',
+              data: await fs.readFile('companion-agent/bin/corrosion-companion-windows-amd64.exe')
+            });
+
+            // Upload checksums
+            await github.rest.repos.uploadReleaseAsset({
+              owner: context.repo.owner,
+              repo: context.repo.repo,
+              release_id: release.data.id,
+              name: 'checksums.txt',
+              data: await fs.readFile('companion-agent/bin/checksums.txt')
+            });
+
+            console.log('Uploaded all release assets');
+
+      - name: Build Summary
+        run: |
+          echo "## 🚀 Companion Agent Build Complete" >> $GITHUB_STEP_SUMMARY
+          echo "" >> $GITHUB_STEP_SUMMARY
+          echo "**Version:** ${{ steps.version.outputs.VERSION }}" >> $GITHUB_STEP_SUMMARY
+          echo "**Commit:** ${GITHUB_SHA:0:7}" >> $GITHUB_STEP_SUMMARY
+          echo "" >> $GITHUB_STEP_SUMMARY
+          echo "### Built Artifacts:" >> $GITHUB_STEP_SUMMARY
+          echo "- ✅ Linux AMD64 ($(stat -f%z companion-agent/bin/corrosion-companion-linux-amd64 2>/dev/null || stat -c%s companion-agent/bin/corrosion-companion-linux-amd64) bytes)" >> $GITHUB_STEP_SUMMARY
+          echo "- ✅ Windows AMD64 ($(stat -f%z companion-agent/bin/corrosion-companion-windows-amd64.exe 2>/dev/null || stat -c%s companion-agent/bin/corrosion-companion-windows-amd64.exe) bytes)" >> $GITHUB_STEP_SUMMARY
+          echo "- ✅ SHA256 checksums" >> $GITHUB_STEP_SUMMARY