chore: rewrite READMEs purpose-first and drop the build script for prepack

[dinwwwh]

Rewrites every README to open with what the project and each package are for, and lines them up with the orpc README shape: centered title, badge block (codecov, npm downloads, MIT license, Discord, DeepWiki), package table, and a License footer. Also removes the redundant build script from the downgrader so prepack alone drives publishing, and adds the MIT LICENSE file the packages already declared.

Docs

• Root README explains the project and lists both packages with one-line purposes, replacing a bare "OAS" title over the sponsors list.
• Package READMEs lead with the package name and purpose. Downgrader mappings use shorter table cells and bullet lists, and document two behaviors the old text missed: path parameters gain required: true, and empty required arrays are dropped.
• Generated sponsors sections are byte-identical. sync-sponsors runs end to end and reports zero changes with the new License section after it.

Packaging

• pnpm pack on the downgrader still runs unbuild via prepack; nothing in docs or CI referenced build.
• LICENSE makes the shields license badge resolve. npm download badges read "not found" until first publish.
• CodSpeed badge left out: the repo has no benchmarks or CodSpeed project yet.

Testing

• ESLint passes on all READMEs.
• README code samples verified: the types example type-checks, the downgrader example produces the documented output.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

📢 Thoughts on this report? Let us know!

[pullfrog]

✅ No new issues found.

I read the full diff (all 6 files) and verified the substantive claims in it against the repo:

• build script removal is safe. I grepped every script, workflow, and config in the repo (CI not building, no docs/lint-staged references) — nothing referenced the build script. prepack: unbuild still drives pnpm pack/publish, and now matches the types package exactly.
• Newly documented downgrader behaviors check out against source and tests: path parameters gain required: true (v3.1-to-v3.0.ts convertParameterOrHeader, tested at v3.1-to-v3.0.test.ts:443), empty required arrays dropped (tested at :1186), format: byte/binary only when no format exists (convertContentKeywords), const: null → nullable: true (convertConst), and multi-type anyOf variants each nullable when null was listed (applyTypes).
• Types README claims check out: @deprecated tags exist in the v3.1/v3.2 sources, style literals are version-specific, the tests/schema/fail corpus is indeed not committed, and the downgrader corpus tests reuse the fixtures as claimed.
• The function-signature table matches the actual exports (notably downgradeSchemaV31ToV30 returning SchemaObject | ReferenceObject).
• ESLint passes clean on all four changed READMEs.

The LICENSE year (2026) matches the repo's release window, and the new README content is accurate, self-contained, and internally consistent. Merge when ready.

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