Prevent save restores from disabling Background Life NPCs

[RANGROO]

Problem

Loading/restoring a save forcibly set background_life_enabled to false for every enrolled NPC. Their database rows remained, but they disappeared from the active Background Life roster.

Fix

• stop save restoration from disabling all Background Life NPCs
• add an idempotent migration that re-enrolls affected NPCs which still have automatic actions, letters, or tracking enabled

Related PR

• unstable: Prevent save restores from disabling Background Life NPCs #681

Validation

• php -l debug/db_updates.php
• php -l lib/core/npc_master.class.php
• git diff --check
• patch verified identical to the focused unstable hotfix
• local migration completed successfully in chim.log
• live Background Life API returned 72 enrolled NPCs after repair

Deployment

• The exact hotfix is active in the local HerikaServer runtime through the current integrated deployment.