P2: Cut 1.0.0 + schema stability / deprecation policy

[dkijania]

Problem

The package is still pre-1.0 (0.0.6) with no documented schema stability or deprecation policy. Public consumers need stability guarantees.

Proposal

• Cut 1.0.0.
• Document a GraphQL schema stability + deprecation policy (graphql-inspector already provides breaking-change enforcement in CI).

Acceptance

• 1.0.0 released; a written stability/deprecation policy exists and is referenced from the README.

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Part of #163.