docs(readme): simplify intro, drop quants/ML-engineer framing

[helloiamvu]

Summary

• Replace the long intro paragraph (README line 13) with a two-sentence version: what the SDK is, what ships today (weather + prediction-market settlements), and the local-first / no-API-key point.
• Simplify the bold tagline (line 3) from "The public-data SDK for quants, ML pipelines, and AI agents." to "A Python + TypeScript SDK for public data."
• Drops the "quants, ML engineers" audience framing everywhere, plus the exhaustive adapter lists and the "Next: SEC filings (EDGAR)..." roadmap sentence.

Docs-only change — no code, no public API surface (TS Parity: N/A).

Test plan

• Verify greps: "quants, ML" and "SEC filings (EDGAR)" no longer appear in README.md; new intro strings present.
• Pre-push hooks (full TS workspace test + typecheck) passed locally.

🤖 Generated with Claude Code

[github-actions]

Parity ticket gate: PASSED

parity-ticket-check: PR does not touch parity-trigger surface; gate skipped.

See CROSS-SDK-SYNC.md §2 for the workflow.