KDL syntax freeze for 1.0 stability

[pesap]

Description

Lock KDL syntax at 1.0. No breaking changes post-1.0.

Tasks:

• Formal grammar documentation
• Version marker in KDL files: `(version "1.0")`
• Backward compatibility guarantee documented
• Archive of all KDL versions migration guides

Acceptance Criteria

• KDL syntax documented formally
• Version marker enforced by parser
• Breaking change policy documented

Context

Part of v1.0 (Stable). Commitment to stability.

Target: v1.0