Update Windows cross-compilation documentation [PM-30733]

[iinuwa]

🎟️ Tracking

PM-18325
PM-29782
PM-29784
PM-30733

📔 Objective

Updates the contributing docs to show new features for building Appx on Windows:

• Cross-compile and sign Windows Appx from macOS (Enable cross-compilation and packaging of Windows Appx from macOS clients#17976)
• Allow local Appx signing on Windows developer machines (Allow local Electron app signing for Windows dev builds [PM-18325] clients#17973)
• Updates signing certificate publisher name (Sign Appx in CI clients#17975)

⏰ Reminders before review

• Contributor guidelines followed
• All formatters and local linters executed and passed
• Written new unit and / or integration tests where applicable
• Protected functional changes with optionality (feature flags)
• Used internationalization (i18n) for all UI strings
• CI builds passed
• Communicated to DevOps any deployment requirements
• Updated any necessary documentation (Confluence, contributing docs) or informed the documentation
  team

🦮 Reviewer guidelines

• 👍 (:+1:) or similar for great changes
• 📝 (:memo:) or ℹ️ (:information_source:) for notes or general info
• ❓ (:question:) for questions
• 🤔 (:thinking:) or 💭 (:thought_balloon:) for more open inquiry that's not quite a confirmed
  issue and could potentially benefit from discussion
• 🎨 (:art:) for suggestions / improvements
• ❌ (:x:) or ⚠️ (:warning:) for more significant problems or concerns needing attention
• 🌱 (:seedling:) or ♻️ (:recycle:) for future improvements or indications of technical debt
• ⛏ (:pick:) for minor or nitpick changes

[github-actions]

Checkmarx One – Scan Summary & Details – 898c994b-a491-45a1-add2-a2b20214aa6f

New Issues (1)

Checkmarx found the following issues in this Pull Request

#	Severity	Issue	Source File / Package	Checkmarx Insight
1		CVE-2026-21884	Npm-react-router-5.3.4	details Recommended version: 7.12.0 Description: A XSS vulnerability exists in in React Router's "" API in Framework Mode when using the "getKey/storageKey" props during Server-... Attack Vector: NETWORK Attack Complexity: LOW Vulnerable Package