docs: add standalone SMT reconstruction specification

[johndauphine]

Summary

Add RECREATE_SMT.md, a standalone, language-agnostic specification for reconstructing SMT’s deterministic schema-migration and DDL subsystem without access to the original repository. It defines normative observable contracts, safety invariants, dialect capabilities, artifacts, CLI/public API behavior, and acceptance criteria while leaving implementation language and internal architecture open.

Impact

This is documentation only. It gives implementers a self-contained compatibility target and does not change runtime behavior.

Validation

• Verified the commit is exactly one file ahead of origin/main and adds only RECREATE_SMT.md.
• Confirmed the worktree is clean and the document includes explicit acceptance and validation criteria for the reconstructed subsystem.

[Copilot]

Pull request overview

Adds a new standalone specification document (RECREATE_SMT.md) that defines the observable contracts and acceptance criteria for reconstructing SMT’s deterministic schema-migration + DDL subsystem without relying on the current repository or implementation language.

Changes:

• Introduces a comprehensive, normative “reconstruction spec” covering deterministic DDL generation, drift/sync behavior, artifacts/manifests, capability gating, and safety invariants.
• Documents the public connection-free DDL/evolution API and dialect capability matrices (PostgreSQL, SQL Server, MySQL, SQLite, ClickHouse).
• Defines compatibility contracts for snapshots/state, CLI surface (commands/flags/exit codes), and optional AI boundaries (parse/review only; never author executable DDL).

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