Add integration action next steps

[Dkm0315]

Summary

• appends integration_next=... after integration setup/verify/enable/sample actions so the workflow keeps using the same /integrations vocabulary
• lifts integration_next into a visible Next row in chat action cards
• keeps native channel/plugin/MCP command output unchanged for diagnostics and failure evidence

Validation

• pnpm exec tsx --test packages/cli/test/cli.test.ts
• pnpm --filter @musterhq/cli build
• smoke: node packages/cli/dist/index.js chat '/integrations sample gchat'
• smoke: node packages/cli/dist/index.js integrations verify parallel-search
• smoke: node packages/cli/dist/index.js integrations verify gchat