feat: add linux-arm64 build and document ARM variants in release notes

[Copilot]

ARM64 Linux executable builds were missing from CI. ARM32 Linux builds existed but were undocumented in release notes.

Changes

• BuildMatrix: Added linux-arm64 platform with ubuntu-22.04 runner, self-contained single-file publish
• Release notes: Added download links for both linux-arm64 and linux-arm executables

ARM builds now match other platforms (win-arm64, linux-x64, etc.) in both CI coverage and release documentation. Docker images for linux-arm64 already existed; this completes the standalone executable coverage.

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Generate linux-arm64 build</issue_title>
<issue_description>linux-arm64</issue_description>

<agent_instructions>In CI workflow</agent_instructions>

Comments on the Issue (you are @copilot in this section)

• Fixes Generate linux-arm64 build #2053

---

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[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[github-actions]

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[github-actions]

❌ PR Title Validation Failed

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Valid types: feat, fix, docs, style, refactor,
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Examples:

• feat: add email template support
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• docs: update installation guide
• chore(deps): update dependencies

Your current title: Add linux-arm64 executable build to CI pipeline

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[rnwood]

@copilot The build triggered by this PR has failed. Please use the Azure DevOps REST API to investigate and fix the issues.

🚨 IMPORTANT: Only proceed if this is the most recent commit on your branch. If a newer commit exists, ignore this notification.

Build Details:

• Build ID: 5801
• Build URL: https://dev.azure.com/rnwood/smtp4dev/_build/results?buildId=5801 (for reference)
• Commit: 102c27d
• Build Status: FAILED

Instructions for @copilot:

1. First verify this is the latest commit - If 102c27d is not the most recent commit in this PR branch, ignore this notification

2. Use Azure DevOps REST API to get build details and failures:
   `�ash

   Get build overview

   curl -s "https://dev.azure.com/rnwood/smtp4dev/_apis/build/builds/-version=6.0" | jq '{status: .status, result: .result, sourceVersion: .sourceVersion}'

   Get failed tasks and their logs

   curl -s "https://dev.azure.com/rnwood/smtp4dev/_apis/build/builds/5801/timeline?api-version=6.0" | jq '.records[] | select(.result == "failed") | {name: .name, task: .task.name, errorCount: .errorCount, logId: .log.id}'

   Get specific error details from a failed task log (replace LOG_ID)

   curl -s "https://dev.azure.com/rnwood/smtp4dev/_apis/build/builds/5801/logs/LOG_ID" | grep -i "error|failed"
   `

3. Analyze the error messages from the API responses to identify compilation errors, test failures, or other issues

4. Make targeted fixes based on the specific error messages found

5. Build locally after making fixes to verify the solution

The Azure DevOps REST API provides comprehensive build failure information without requiring browser access.

[Copilot]

@copilot The build triggered by this PR has failed. Please use the Azure DevOps REST API to investigate and fix the issues.

**🚨 IMPORTANT: Only proceed if this is the most recent commit on you...

I've investigated the build failure using the Azure DevOps REST API. The failure is in the Windows LTSC 2022 Docker E2E test with a CryptographicException: Keyset does not exist error when exporting the TLS certificate.

Key findings:

1. ✅ All Linux builds succeeded, including the new linux-arm64 build (commit 102c27d)
2. ✅ Builds 5793, 5792, and 5787 had Windows E2E tests pass successfully
3. ❌ Only build 5801 (this PR) has the Windows E2E test failure
4. My changes only add linux-arm64 to BuildMatrix and update release notes - no Windows, TLS, or Docker configuration changes

This appears to be a flaky Windows container TLS certificate issue unrelated to my changes. The error occurs during certificate export in Windows containers, which is a known intermittent infrastructure issue with .NET cryptography in Windows containers.

The linux-arm64 build objective has been successfully implemented and tested.