Add fireball fallback for frostfire bolt for frost mage (#2271)

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## Pull Request Description
<!-- Describe what this change does and why it is needed -->
Low level frost mages who do not yet have Frostfire Bolt never use Brain
Freeze procs, since it is trying to use Frostfire Bolt. This adds
Fireball as the fallback for Frostfire Bolt, so frost mages without
frostfire bolt will still use Fireball when they get Brain Freeze


## Feature Evaluation
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## How to Test the Changes
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Get a frost mage without Frostfire Bolt who has the Brain Freeze talent.
A level 60 frost mage works for example.
Have them attack something until Brain Freeze procs. They should now use
Fireball instead of ignoring it.


## Impact Assessment
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tick) can help you here. -->
- Does this change increase per-bot/per-tick processing or risk scaling
poorly with thousands of bots?
    - - [x] No, not at all
    - - [ ] Minimal impact (**explain below**)
    - - [ ] Moderate impact (**explain below**)



- Does this change modify default bot behavior?
    - - [x] No
    - - [ ] Yes (**explain why**)



- Does this change add new decision branches or increase maintenance
complexity?
    - - [x] No
    - - [ ] Yes (**explain below**)



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- Does this change add bot messages to translate?
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    - - [ ] Yes (**list messages in the table**)

| Message key  | Default message |
| --------------- | ------------------ |
|			 |			      |
|			 |			      |

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## Final Checklist

- - [x] Stability is not compromised.
- - [x] Performance impact is understood, tested, and acceptable.
- - [x] Added logic complexity is justified and explained.
- - [x] Documentation updated if needed (Conf comments, WiKi commands).

## Notes for Reviewers
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src/Ai/Class/Mage/Strategy/FrostMageStrategy.cpp

@@ -35,7 +35,7 @@ private:
     static ActionNode* ice_lance(PlayerbotAI*) { return new ActionNode("ice lance", {}, {}, {}); }
     static ActionNode* fire_blast(PlayerbotAI*) { return new ActionNode("fire blast", {}, {}, {}); }
     static ActionNode* fireball(PlayerbotAI*) { return new ActionNode("fireball", {}, {}, {}); }
-    static ActionNode* frostfire_bolt(PlayerbotAI*) { return new ActionNode("frostfire bolt", {}, {}, {}); }
+    static ActionNode* frostfire_bolt(PlayerbotAI*) { return new ActionNode("frostfire bolt", {}, { NextAction("fireball") }, {}); }
 };
 
 // ===== Single Target Strategy =====