fix(DB): rename structure.sql to fix duplicate filename CI error

[Nyeriah]

Summary

• Renames data/sql/db-world/structure.sql to data/sql/db-world/mod_ptrtemplate_structure.sql
• The AzerothCore DB updater requires all SQL filenames to be unique across the entire project (core + all modules)
• The generic name structure.sql causes a duplicate filename collision during the nopch-module-build CI job on azerothcore-wotlk, which has been failing since at least March 29th

CI Error

Duplicate filename ".../modules/mod-ptr-template/data/sql/db-world/structure.sql" occurred.
Because updates are ordered by their filenames, every name needs to be unique!
Could not update the World database, see log for details.

Test plan

• Verify nopch-module-build CI passes on azerothcore-wotlk after this merge
• Verify module installs cleanly with the renamed SQL file

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