hardening: migrate cycle SQL helpers to prepared variants

[somethingwithproof]

Problem

plugin_cycle still has raw SQL helper calls (db_fetch_row, db_fetch_cell, db_fetch_assoc, db_execute) in setup and runtime paths.

Proposed change

• migrate straightforward SQL helper sites to prepared variants
• parameterize values currently interpolated into SQL where applicable
• preserve existing plugin behavior

Tests

• add standalone regression checks for converted prepared helper usage
• run syntax checks for modified files and the test script