docs: align v1.1.0 Commons docs to flat schema contract

[GsCommand]

Motivation

• Make repository documentation authoritative and presentation-ready for the v1.1.0 flat Commons schema family by removing legacy/x402/trace framing and stale examples.
• Ensure quickstart and validation guidance are accurate and point to the actual working commands and schema layout.
• Clarify the trust model to match the schemas' hash+signature receipts and explicitly mark v1.0.0 as legacy.

Description

• Updated README.md to remove legacy trace/x402 framing, replace stale examples with real v1.1.0 request/receipt fields, change CID: PENDING to CID: TBD (pre-release), and replace the broken npx cl-validate guidance with working npm/node validation commands and examples.
• Added a dedicated Commons v1.1.0 section to SPEC.md that defines the flat request shape and the proof-oriented receipt shape (fields: verb, version, status, timestamp, request_hash, optional result_hash/result_cid, summary on success, signature, error on failure), and marked v1.0.0 as legacy and structurally different.
• Rewrote SCHEMAS.md to document the current flat schemas/v1.1.0/commons/<verb>/ layout, update deterministic $id examples to the v1.1.0 pattern, remove references that implied nested requests/ and receipts/ in v1.1.0, and align validation guidance with the repository scripts.
• Files modified: README.md, SPEC.md, SCHEMAS.md.
• Noted remaining inconsistencies: manifest.json still contains "schemas_cid": "PENDING" and checksum-generation scripts default to schemas/v1.0.0, which may be surprising given v1.1.0 is the current layout.

Testing

• Ran repository validation: npm run validate (this runs validate:schemas and validate:examples); result: all schemas compiled and all examples for both v1.0.0 and v1.1.0 validated successfully (no failures).
• Verified scripts/validate-all.mjs and scripts/validate-examples.mjs run cleanly in Ajv 2020-12 strict-style configuration; outcome: success.

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Codex Task