docs: state 0.7.5 stable and 0.7.6 preview, rewrite the specification against 0.7.5, and make every example validate

[fas89]

Re-cut onto main after #50 merged: one signed-off commit whose tree is exactly the reviewed branch (delta compared byte-for-byte). It touches docs/** and README.md only.

What this changes

A truth pass over the spec site's documentation, measured against the schemas #50 publishes (0.7.5 stable, 0.7.6 preview) and against how the reference implementation (data-product-forge 0.18.1) behaves.

• Version and status model.
  • README.md, docs/schema/versions.md and docs/releases/README.md say 0.7.5 is the latest stable version and 0.7.6 is a preview: what "preview" means, how a contract opts in, and that a preview can change until it is promoted.
  • versions.md records that the published 0.7.1 and the reference implementation's 0.7.1 differ under the same $id.
• 0.7.6 notes. A new docs/releases/0.7.6.md (preview), derived from the 0.7.6 schema itself.
  • It covers packaging, consumers, consumes[].upstreamWorkspace / upstreamDigest (tied by dependentRequired), measures[].aggParams, binding.encryption.kms, exposes[].lifecycle.expire, binding.principals and lakeFormation.bucketPolicy.
  • It has a danger box: an emitted bucket policy is authoritative and replaces every other statement on the bucket.
• 0.7.5 notes. The release note covers the GA additions (pgvector, vectorConfig, Iceberg catalog location, Redshift Serverless / Kinesis). Its headline example did not validate and now does.
• Changelog. Gains 0.7.4→0.7.5 and 0.7.5→0.7.6, and fixes earlier entries that described the wrong version's history.
• specification.md.
  • Its body still described schema 0.0.1; it is rewritten against 0.7.5 and kept a specification.
  • The multi-file composition section recommended a .fluid/ directory, which is the reference implementation's runtime state directory. It now gives an accurate, explicitly non-normative description:
    • a composed root is not itself a FLUID document; validate the resolved document;
    • the reference implementation's fragments/ layout;
    • its 0.18 confinement rules;
    • links to the forge docs for fluid split / fluid bundle.
• Anatomy, cheatsheet, minimal contract. Invalid examples are fixed, and every example YAML now validates against the version it declares. Lake Formation admins carries the authoritative warning: unlisted admins are removed, and destroying the resource empties the list.
• Smaller fixes.
  • docs/concepts/forge-cli.md: the package is data-product-forge, and the page states version support and the composition commands.
  • The modular-layout deck slide is corrected.
  • The fluidVersion guidance is corrected.
  • The contributing page says what the drift job does.
  • Licence mentions match LICENSE (Apache 2.0).

The spec stays neutral: forge-cli is described as the reference implementation, and nothing here changes which documents validate.

Tested

• npm run docs:build succeeds.
• The base-prefix link check from conformance.yml finds no internal absolute link without /fluid/.
• Every YAML example in the changed pages was validated with jsonschema (2020-12) and with fluid validate (0.18.1), against the schema version it declares.
• Live: I served the built site under /fluid/ and opened it in a browser.
  • The versions page shows 0.7.6 as a preview and 0.7.5 as latest stable.
  • The specification's composition section shows the fragments/ layout and links the forge docs.
  • No console errors.

Security review

The review covered both PRs; findings that belong to docs are fixed here. They are the bucket-policy danger box, the completed admins warnings and accurate drift-check wording.

Commits are DCO signed-off.