fix(web): copy multi-output workflow results

[officialasishkumar]

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Summary

Fixes #34632.

Published Workflow WebApp runs with multiple output fields serialize the full result into the Detail content while workflowProcessData.resultText remains empty. The action bar only showed copy for workflow Result-tab text, so multi-output workflow results had no usable main copy action.

This change exposes the workflow copy action on the Detail tab when serialized output exists, and makes workflow copy content fall back to that serialized output when resultText is empty. It keeps the existing single-string Result-tab behavior unchanged.

Screenshots

Before	After
Multi-output workflow Detail output had no main copy action.	Detail output exposes the copy action and copies the serialized JSON result.

Checklist

• This change requires a documentation update, included: Dify Document
• I understand that this PR may be closed in case there was no previous discussion or issues. (This doesn't apply to typos!)
• I've added a test for each change that was introduced, and I tried as much as possible to make a single atomic change.
• I've updated the documentation accordingly.
• I ran make lint and make type-check (backend) and cd web && pnpm exec vp staged (frontend) to appease the lint gods

Validation

• PATH=/home/sarthak/.npm/_npx/54df5c7b67c3fbcf/node_modules/node/bin:$PATH ../node_modules/.bin/vp test app/components/app/text-generate/item/__tests__/action-groups.spec.tsx app/components/app/text-generate/item/__tests__/utils.spec.ts
• PATH=/home/sarthak/.npm/_npx/54df5c7b67c3fbcf/node_modules/node/bin:$PATH ../node_modules/.bin/vp run lint:ci app/components/app/text-generate/item/action-groups.tsx app/components/app/text-generate/item/utils.ts app/components/app/text-generate/item/__tests__/action-groups.spec.tsx app/components/app/text-generate/item/__tests__/utils.spec.ts
• PATH=/home/sarthak/.npm/_npx/54df5c7b67c3fbcf/node_modules/node/bin:$PATH NODE_OPTIONS=--max-old-space-size=8192 ../node_modules/.bin/vp run type-check
• pre-commit hook completed: ESLint autofix, type-check:tsgo, and knip