fix(tally): require parent for ledger creates

[lamemustafa]

Summary

Fixes #51: reject a controlled ledger create without an explicit parent before it can be previewed or authorized. This keeps the existing alter-state model intact and extends the synthetic XML-escaping test to cover the required parent.

Validation

• cargo fmt --all --check
• cargo test -p bridge-tally-write
• cargo clippy -p bridge-tally-write --all-targets -- -D warnings
• cargo check --workspace
• git diff --check

Migration and rollback

No database migration or sync-behavior migration. No live Tally request or write was made. Roll back with git revert 0a671d2.

Security impact

Tally write-qualification change: it narrows the accepted payload set and adds no endpoint, credential, raw-data, or logging path.

Review checklist

• Errors are actionable without exposing sensitive values
• No secrets, credentials, personal data, or customer data are included
• Tally changes include explicit security impact notes
• Shared build and check commands pass without shell-specific syntax
• Existing workflow changes include rollback and migration compatibility

[lamemustafa]

@codex review

[chatgpt-codex-connector]

Codex Review: Didn't find any major issues. Nice work!

Reviewed commit: 0a671d27a4

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