[codex] use reusable GitHub workflows

[saagpatel]

What

• Converts copied hygiene/performance/lockfile workflows to reusable workflow callers.
• Pins callers to saagpatel/sovereign commit d20fe9e542f3efd545e0135dee4b4314b6af56a6.

Why

• Removes drifted inline workflow copies and closes unpinned workflow-action supply-chain surface.

How

• Replaces target workflow bodies with thin workflow_call callers.

Testing

• Parsed workflow YAML locally before commit.
• Repo hooks ran during commit/push.

Performance impact

• CI-only workflow consolidation; no runtime impact.

Risks

• Depends on sovereign PR build(deps): bump picomatch from 2.3.1 to 2.3.2 #43 / pinned commit availability.

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