[IR-P7][WS6] Complete release readiness and v0.13.0 deprecation-target validation

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Problem statement

Phase 7 deliverable 3 needs a dedicated issue to finalize release readiness while ensuring deprecation messaging consistently targets v0.13.0.

Intended invariant

Release branch is green and all deprecation warnings/docs consistently target v0.13.0 for hard removal.

Scope boundaries

• Implements only this Phase 7 deliverable
• Covers release checklist/changelog and warning-target validation
• Excludes actual removal of deprecated paths (Phase 8)

Deliverable checklist

• Implementation complete for this deliverable
• Tests/verification checks passing
• Migration impact recorded with rationale
• Docs impact recorded with required updates landed
• Evidence linked for roadmap phase gate

Validation plan

Run release readiness checks + deprecation-target consistency checks and attach evidence.

Parent epic

#100

Roadmap reference

Roadmap reference: docs/plans/2026-06-19-001-ir-first-roadmap.md (Phase 7)

Migration impact

minor - no removal in this phase; messaging and readiness validation only.

Documentation impact

update-existing - release and migration docs must reflect compatibility-window behavior.

Sync status

Synced with roadmap: 2026-06-19