hardening: G11 enforce production demo-mode guardrail

[DevCalebR]

Summary

• add shared production demo-mode guardrail helper
• block production demo mode unless ALLOW_PRODUCTION_DEMO_MODE=true is explicitly set
• enforce guardrail in both env validation and middleware fail-safe path
• extend env preflight checks for demo-mode production safety
• add unit tests and docs updates for break-glass behavior

Validation

• npm test
• npm run lint
• npm run build
• npm run typecheck
• npm run env:check
• npm run db:validate

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Project	Deployment	Actions	Updated (UTC)
callbackcloser	Ready	Preview, Comment	Mar 2, 2026 4:45am