add approval source message links

[dnbrwstr]

Summary

Adds a View message button to approval cards so the owner can jump back to the message that triggered the prompt.

Changes

• add local A2UI navigation action validation for plugin-generated blobs
• include source-message navigation on DM and channel approval cards
• keep group invite cards unchanged because they do not have a triggering message

How did I test?

• pnpm exec vitest run src/monitor/approval.test.ts
• pnpm build
• local web demo with DM and channel approval cards, including clicking the channel View message button

[patosullivan]

Migrated to the tlon-apps monorepo: tloncorp/tlon-apps#5940 (cherry-picked onto the rebased a2ui stack, relocated to packages/openclaw). Closing in favor of that PR.