Update Astro dependency set to latest and migrate Starlight sidebar config for v0.39

[Copilot]

• Verify what security-related changes are currently in the PR
• Confirm whether dependency updates already address known vulnerabilities
• Remove GitHub workflow edits so this PR only contains site-related changes
• Re-run build validation
• Re-run final validation checks

Original prompt

Update all npm dependencies in package.json to their latest versions:

• @astrojs/starlight: Currently ^0.35.3, update to latest
• astro: Currently ^6.3.6, update to latest
• sharp: Currently ^0.34.3, update to latest

This will ensure the website is using the most recent versions of all dependencies, including the recent Dependabot update for astro and all other packages.

The following is the prior conversation context from the user's chat exploration (may be truncated):

User: Dependabot updated astro in my website repo, but other dependencies also need updating, can you do this? Update everything to latest.

Assistant: I'd be happy to help update all dependencies in your website repo! However, I need a bit more information:

1. Repository name: What's the name of your website repository? (e.g., my-website, portfolio, etc.)
2. Repository owner: Is this under your personal account (Boxersteavee) or an organization?

Once you provide these details, I can update all dependencies to their latest versions.

User: Repo is 'website', under my personal account

Assistant: Now let me create a pull request to update all dependencies to their latest versions:

Assistant: I'm waiting for your confirmation to proceed with creating a pull request that updates all dependencies in your website repository to their latest versions.

This pull request was created from Copilot chat.