[Blog] Release 0.13.0 report and upgrade guide

[chalin]

• Contributes to Release 0.13.0 preparation #2266
• Adds "Release 0.13.0 report and upgrade guide"
• Consolidates the 0.13.0 CL entry, mostly referring to the release report
• Makes some tweaks to and cross-references with the 0.12.0 blog post
• Improves sections of the UG for features in scope of this release

Preview: https://deploy-preview-2368--docsydocs.netlify.app/blog/2025/0.13.0/

[chalin]

@LisaFC et all: I'm going to factor out everything that isn't the 0.13.0 blog and submit it separately so that this PR can be more focused.

[chalin]

@LisaFC - the non-blog post content is in:

• UG adjustments to existing content, and task-file updates pre-0.13.0 #2369

I'll merge that separately, and remove it from this PR.