docs: improve release process documentation

[andygrove]

Summary

• Add a quick-reference checklist at the top of the document
• Add a release preparation section covering expression support review
• Make version numbers consistent throughout (using 0.13.0 as the example release)
• Add prerequisites for create-tarball.sh (GPG key, SVN credentials, Python requests package)
• Add link to verification guide and verify-release-candidate.sh script
• Add guidance for when a vote fails (increment RC number, repeat from tagging)
• Add announcement email content guidance
• Clean up /comet:$ prompt artifacts in publish-to-maven.sh examples
• Consolidate "Post Release Admin" and "Post Release Activities" into a single "Post Release" section
• Remove outdated "Publishing Crates" section
• Remove "Update released version number in documentation" section (now dynamic)
• Clarify that some tasks require PMC membership while preparation tasks are open to any contributor

Test plan

• Verify the document renders correctly in the docs build
• Review all version number references for consistency

🤖 Generated with Claude Code

[andygrove]

@comphead I added some notes on checking that documentation is up to date before starting the release process, based on your suggestion.

[comphead]

we should probably mention that commands to execute checklist items are below.

btw to avoid chasing versions WDYT if we have template for this doc, where we would define current_version and next_version and script that generates actual md file replacing current_version and next_version with actual values 0.13, 0.14?

[andygrove]

oops, missed this comment ... 0.13.0 is just used as an example - no need to update this each time. Previously there was a mix of versions, so it was confusing.

We do have something like $COMET_VERSION substitution already in docs.

[comphead]

Thanks @andygrove