chore: remove tegami release process

[gabrielmfern]

Reverts #999, #1002, #1007, #1010, and #1026.

Reverting because using it was a bit of an internal experiment to see if it was a good fit. Though I feel it was a good fit, there are some details around prereleases we need to figure out, and there's no time for that now, so we're reverting it until we've properly explored and more widely discussed it internally as an option.

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Summary by cubic

Remove the Tegami release process and revert to the previous release workflow. This deletes Tegami CI workflows and config, and drops the tegami dependency.

• Refactors
  • Removed GitHub workflows: release.yml, version.yml, tegami-pr.yml, tegami-pr-comment.yml.
  • Deleted .tegami/publish-lock.yaml and scripts/tegami.mts.
  • Removed tegami script and dependency from package.json; updated lockfile and pnpm-workspace.yaml.
  • Releases return to the prior process; no prerelease automation via tegami.

^{Written for commit 5e7f89e. Summary will update on new commits.}

[cubic-dev-ai]

No issues found across 9 files

Confidence score: 5/5

• Automated review surfaced no issues in the provided summaries.
• No files require special attention.

<sub>Auto-approved: Removes the experimental tegami release process and reverts to the prior workflow; a bounded, clearly beneficial rollback with no new behavior or operational tradeoffs introduced.

Re-trigger cubic</sub>

[ranisalt]

This has removed provenance which will cause a trust downgrade error for everyone using a package manager that checks for supply chain policies (e.g. pnpm)