feat: add business-flex profiles, budgets, and routing visibility

[richard-devbot]

Summary

• Adds profile-based RStack activation for business teams (business-flex, enterprise-webapp, lean-mvp)
• Adds project-local .rstack/rstack.config.json and .rstack/budget.json generation through rstack-agents init --profile
• Adds requirements/planning-stage budget policy loading, task-level budget envelopes, and routing explanations
• Adds optional Contract v2 execution/cost/context/routing telemetry to builder contracts while preserving backward compatibility
• Adds Business Flex dashboard state and UI from real .rstack profile, budget, and routing data

Test Plan

• npm test -- --runInBand
• npm run lint
• npm run validate
• git diff --check
• npm pack --dry-run

Closes #64
Closes #65
Closes #66
Closes #67

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