fix(Core/Unit): Notify creature pets when owner enters combat via assist

[blinkysc]

Changes Proposed:

This PR proposes changes to:

• Core (units, players, creatures, game systems).
• Scripts (bosses, spell scripts, creature scripts).
• Database (SAI, creatures, etc).

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  • Claude Code with AzerothMCP

Issues Addressed:

• Closes [NPC] Mobs with Pets - Aggro Bug chromiecraft/chromiecraft#9228

SOURCE:

The changes have been validated through:

• Live research (checked on live servers, e.g Classic WotLK, Retail, etc.)
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Tests Performed:

This PR has been:

• Tested in-game by the author.
• Tested in-game by other community members/someone else other than the author/has been live on production servers.
• This pull request requires further testing and may have edge cases to be tested.

How to Test the Changes:

• This pull request can be tested by following the reproduction steps provided in the linked issue
• This pull request requires further testing. Provide steps to test your changes. If it requires any specific setup e.g multiple players please specify it as well.

1. .go creature id 11882 — teleport to Twilight Stonecaller in Silithus
2. Each Stonecaller should have a summoned Earth Elemental nearby
3. Attack one Stonecaller — nearby Stonecallers will assist via aggro chain
4. Before fix: The assisting Stonecallers' Earth Elementals stand idle
5. After fix: The Earth Elementals join combat with their owners

Known Issues and TODO List:

• Verify this doesn't cause issues with player-owned guardians (the path already exists for player pets via DealDamage and Attack)
• Test with other NPC summoner/pet pairs (e.g. warlocks with void walkers, other caster+elemental combos)

Description

When a creature enters combat via assist or aggro chain (as opposed to being directly attacked), its controlled creatures (guardians/pets summoned via spells like Summon Earth Elemental) were never notified. The existing OwnerAttackedBy notification only fires from DealDamage — meaning only the directly attacked creature's pets would assist.

This adds an OwnerAttackedBy call in Creature::AtEngage so that whenever a creature enters combat for any reason, its controlled creatures are informed about the engage target and can assist.