chore: add Flue deploy workflow on merge to production

[mvvmm]

Summary

Adds a GitHub Actions workflow that automatically deploys the Flue bot Worker (cloudflare-docs-flue) whenever .flue/** changes are merged to production.

• .github/workflows/flue-deploy.yml — new workflow: triggers on push to production (path-filtered to .flue/**), runs pnpm run flue:deploy, uses the existing CLOUDFLARE_API_TOKEN secret, serializes deploys with cancel-in-progress: false, and posts a Google Chat failure alert on error
• package.json — drops --secrets-file .env from flue:deploy; Worker runtime secrets are preconfigured on the Worker and preserved across deploys by Wrangler
• .flue/wrangler.jsonc — adds secrets.required listing all 10 production runtime secrets so wrangler deploy fails explicitly if any are missing
• .github/workflows/ci.yml — adds flue-deploy.yml to paths-ignore so the main docs CI does not run on deploy-workflow-only changes

Documentation checklist

[github-actions]

This pull request requires reviews from CODEOWNERS as it changes files that match the following patterns:

Pattern	Owners
*	@cloudflare/product-owners
/.github/	@cloudflare/content-engineering, @kodster28, @mvvmm, @colbywhite, @ahaywood, @MohamedH1998
package.json	@cloudflare/content-engineering

[github-actions]

Preview URL: https://334ad134.preview.developers.cloudflare.com
Preview Branch URL: https://flue-deploy-workflow.preview.developers.cloudflare.com