Cut v1.0.0 (API freeze)

[yancya]

Background

v1.0.0 is the API-freeze release: after v0.5.0 ships and the consistency matrix (#23) pins down cross-backend behavior, declare the public API (create_relation_literal(schema, tuples) on the three backend modules) stable.

Prerequisites

• v0.5.0 released and soaked briefly (no bug reports against the new behavior)
• Cross-backend edge-case consistency test matrix #23 (consistency test matrix) closed
• Human GO required for the tag push, same as every release.

Acceptance criteria

• Final README pass: all three backends documented at equal depth; Errors / edge-case behavior section reflects the matrix in Cross-backend edge-case consistency test matrix #23; examples copy-paste runnable
• Explicit statement in README of what the stable API surface is (module names, method, error classes) and the SemVer promise from 1.0 onward
• required_ruby_version (from Add gemspec metadata, required_ruby_version, and a CHANGELOG #16) still matches CI matrix; drop or add Ruby versions consciously and note it in the CHANGELOG
• Version bumped to 1.0.0, CHANGELOG entry written
• Tag v1.0.0 pushed (human GO), release workflow single green run, gem on rubygems.org

Verification

• gem list relationizer --remote shows 1.0.0
• README audit: every documented example executed in bin/console matches its #=> comment

[yancya]

このセッションでは着手をスキップします。理由: v1.0.0 のタグ push はリリース行為(デプロイ相当)であり、事前の /goal 指示でスキップ対象と明示されているため。

加えて前提条件(#24 のリリース完了、#23 のクローズ)が現時点で未達です。#23 は本セッションで着手予定ですが、#24 はユーザー GO 待ちのため、本 issue は当面着手不可の状態です。