fix: Inferno Titan trigger cannot divide damage

[jonathanchang31]

Summary

This PR solve the issue #3681

Related Issue

Closes: #3681

Change Type

• Bug Fix (Investigation & Resolution)
• New Feature
• Breaking Change
• Refactoring
• Tests Added
• Performance

[gemini-code-assist]

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[matthewevans]

VERDICT: request-changes

[HIGH] This PR adds intentional failing diagnostic tests instead of fixing #3681. Evidence: crates/engine/src/game/ability_utils.rs:8786 and crates/engine/tests/integration/zz_inferno_diag.rs:73 both unconditionally panic! after printing debug output. Why it matters: the branch cannot merge because the test suite is deliberately red, and it does not change the production target/distribution behavior for Inferno Titan. Suggested fix: remove the diagnostic-only tests, implement the actual divided-damage target selection fix at the production seam, and add a non-panicking regression that asserts the expected target selection/distribution state.

[MED] The regression currently observes the flow but never asserts the claimed behavior. Evidence: crates/engine/tests/integration/zz_inferno_diag.rs:51-73 loops until a waiting state, prints slot counts, then panics regardless of whether target selection or distribution is correct. Why it matters: this repeats the false-green pattern from #3725 in the opposite direction: it proves neither the bug nor the fix, so it would not protect the engine once the panic is removed. Suggested fix: assert exact state, target count, and distribution affordance for the Inferno Titan trigger, including the one/two/three target choices relevant to CR 601.2d divided damage.