docs: add agentic monetization strategy

[huygdv]

Summary

Adds a strategic note for how Causari should respond to Cloudflare's Monetization Gateway / x402 announcement.

Core decision:

• Treat monetization as a future adapter layer, not the product core.
• Focus first on valuable causal resources: curated events, links, evidence, confidence, insights, MCP/API contracts.
• Keep x402 / Cloudflare as one possible rail, not a hard dependency.

Expert review lenses included

• Founder
• Product owner
• Solution architect
• Security and trust
• Market
• User

Key recommendation

Build toward this order:

valuable resource → stable schema → API/MCP surface → policy/pricing adapter

Notes

This PR is docs-only. It does not change pack schemas or runtime behavior.