feat: prepare embeddable council payload

[Victor "David" Medina (Victor-David-Medina)]

Summary

Adds minimal embeddable CouncilVerse payload support for docs, product surfaces, and websites that need to render a debate shell without binding to a specific LLM provider.

• Adds buildCouncilEmbedPayload() with a stable councilverse.embed.v1 payload shape.
• Adds tests for provider-agnostic agents, synthesis prompt output, trimming, and empty-question rejection.
• Adds a README embed example that runs from the published package entry point.

Verify before claim

check	expected	artifact	runner
npm test	6 files, 133 tests passed	C:\Users\LENOVO-LOQ-RTX4060\.copilot\session-state\3c148841-71a6-4697-ad11-358cded3fb04\files\sprint4-councilverse-tests.txt	Copilot local
npm run build	exit 0	C:\Users\LENOVO-LOQ-RTX4060\.copilot\session-state\3c148841-71a6-4697-ad11-358cded3fb04\files\sprint4-councilverse-build.txt	Copilot local
README embed example	emits councilverse.embed.v1, 5 agents, defaultRounds 2	C:\Users\LENOVO-LOQ-RTX4060\.copilot\session-state\3c148841-71a6-4697-ad11-358cded3fb04\files\sprint4-councilverse-readme-example.txt	Copilot local
git diff --check	exit 0	C:\Users\LENOVO-LOQ-RTX4060\.copilot\session-state\3c148841-71a6-4697-ad11-358cded3fb04\files\sprint4-councilverse-diff-check.txt	Copilot local

Notes

No deployment or publishing. This is code and docs prep only.