Automate release note updates

[danielporterda]

Goal

Automate updates for the release notes published in cf-docs so upstream changes produce small, reviewable PRs instead of manual copy work.

Target issues

• #750 Automate Splice release note updates
• #751 Automate Canton release note updates
• #752 Automate Wallet Gateway release note updates
• #753 Automate Wallet SDK release note updates
• #754 Automate dApp SDK release note updates

Acceptance criteria

• Each target has a repeatable refresh command or workflow, or a documented reason automation is not viable.
• Automation opens or updates a PR only when the published output changes.
• PRs identify the upstream source version/revision and affected page.
• Existing published routes and frontmatter are preserved.

Out of scope

• Rewriting release-note content beyond mechanical formatting needed for publication.
• Automating the Release Notes index, Release History, or Weekly Patch Releases pages unless a target needs link updates there.