Automate Wallet Gateway release note updates

[danielporterda]

Parent: #749

Current state

`docs-main/integrations/release-notes/wallet-gateway.mdx` is copied manually from Wallet Gateway package releases.

Goal

Automate updates for this published release-note page.

Scope

• Source: `@canton-network/wallet-gateway-remote` GitHub releases in `hyperledger-labs/splice-wallet-kernel`.
• Output: docs-main/integrations/release-notes/wallet-gateway.mdx
• Route: /integrations/release-notes/wallet-gateway

Acceptance criteria

• cf-docs has a repeatable command or workflow for refreshing this page.
• The process detects whether the upstream source changed before opening or updating a PR.
• The published route and page frontmatter are preserved.
• The PR body identifies the upstream source revision/version and summarizes changed release-note sections.