Document campaign continuation workflow

[KevinBigham]

What changed

• allow sequential bounded goals to continue within a marathon campaign
• align repository agent guidance and the Codex program ledger
• preserve separate branches, worktrees, dependency ordering, and conflict rules

Why

These edits preserve the user-approved campaign workflow without changing gameplay, saves, schemas, or runtime behavior.

Validation

• git diff --cached --check
• exact three-file staging scope reviewed
• documentation-only change; gameplay gates are unaffected