docs: drop the README versioning section

[jfrench9]

Summary

• Removes the Versioning section from the README. It still described the 1.x contract after the client moved to 2.x; the wiki's Versioning and Compatibility page is the home for that explanation.
• The release-notes command now says the integration template pins "the current major" instead of a hard-coded >=1,<2 that went stale at 2.0.0.
• The Features list names the AI integration "AI Operator", matching the codebase and the TypeScript README, instead of "Financial AI Agent".

Docs and command text only; no code changes.

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