Apply Infernal Cry extra fire to empowered attacks

[unrealdreamz]

Summary

Refs #714

Adds the missing stat mapping for Infernal Cry's empowered attack bonus so its Gain x% of Damage as Extra Fire Damage stat is emitted as a Warcry buff for empowered melee attacks.

Root Cause

Infernal Cry's exported skill data already included infernal_cry_exerted_attack_all_damage_%_to_gain_as_fire_%, and the stat description rendered it for users, but the skill had no statMap entry. The stat therefore never became a live modifier, so enabling Infernal Cry could show no extra fire damage effect on empowered melee attacks.

This PR intentionally does not claim to finish the broader automatic Full DPS / Warcry Power behavior discussed in #714; it fixes the missing damage modifier path only.

Fix

• Add a generated-data and export-source statMap entry for Infernal Cry.
• Emit DamageGainAsFire as a melee-only Warcry global effect.
• Gate the modifier behind the existing Empowered condition so non-empowered attacks are not affected.
• Add a system regression that verifies Infernal Cry now produces a Warcry buff modifier with the melee flag and Empowered condition tag.

Validation

• gh pr list --repo PathOfBuildingCommunity/PathOfBuilding-PoE2 --state open -S '714 Infernal Cry empowered fire' --json number,title,headRefName,author,url --jq '.' -> []
• git diff --check -> passed
• git diff --cached --check -> passed
• git show --check --stat --oneline HEAD -> passed

I did not run Docker/Busted locally in this pass because this machine is currently in active foreground use; the regression is included for CI to run in the repository's normal test container.

Risk / Rollback

Low risk. The change is data-scoped to Infernal Cry and applies only when the active skill is an empowered melee attack. Rollback is reverting this commit, which removes the stat mapping and the regression test.