docs: rewrite README around a runnable quickstart and quirks table

[TheGreatAxios]

Summary

• Opens with an identity and placement line, a "Why" list, and a single install line including the ^0.4.0 peers.
• Quickstart streams one turn through createOpenAIResponsesAdapter and surfaces inference.error.
• Where it fits, an exports table (both provider ids), manifest wiring via loadAdapterRegistry, and Upgrading from 0.1.
• The sidecar manifest paragraph and Grok example give way to a generic responsesAdapterFactory example, which ignores per-source quirks.
• Quirks reference table: type, default and request effect for every field.
• How it works and Development move to CONTRIBUTING.md.
• Stacked on refactor!: trim the barrel and deprecate the 0.1 provider id #15.

Verification

• All snippets typecheck against the built package; the quickstart ran against remote Ollama (qwen2.5:7b).
• Quirks table checked row by row against the resolver and request builder.
• bun run check passes (40 pass, 2 skip).

Closes CL-9228
Closes CL-9237
Closes CL-9240
Closes CL-9242
Closes CL-9246
Closes CL-9250

[TheGreatAxios]

Reviewed against the exports branch. Quickstart typechecks under strict nodenext; every quirks-table row matches the resolver and request builder; peer deps and engines match package.json. check passes. No outstanding findings.