Client: spell cast sync for remote players

[Kheartz]

Remote players' spell casts now replay on their proxies; the cast animation plus the real spell VFX/projectile, aimed in 3D. Stacks on the locomotion/broom wire (the Cast flag + spellId/aimPitch fields were already reserved in human_sync.hpp), so no new netcode bump.

Owning client publishes (UpdateLocal):

• Detects a combat cast via the combat-AnimBP's FullBodyState == 7 (full-body/rooted casts).
• Publishes the Cast flag, which spell as a 1-based id into the spell_records.hpp allowlist (~80 DA_*SpellRecords), and the aim pitch (GetControlRotation().Pitch, clamped ±90 into a signed byte — the on-foot body never pitches, so vertical aim needs its own field).

Remote proxy applies (UpdateCast, on the Cast flag's rising edge):

• Plays a cast montage into the AnimBP's DefaultSlot (over the running locomotion).
• Resolves the synced id → record path, loads it, and fires the real spell via SpellHelper::CastSpell, aimed from synced facing-yaw + the synced pitch (forward = (cosP·cosY, cosP·sinY, sinP)).

The allowlist (range-checked, append-only, 1-based) bounds what a proxy can load — an out-of-range/hostile id just no-ops, never an arbitrary asset load.

Test command: /spawnnpc, t

• Arm pose is generic--only the fired spell's direction follows aimPitch; the cast arm montage is one full-body clip and doesn't bend to the angle. Matching the arm would need an aim-offset/additive pose (tracked as a follow-up, cosmetic).
• v1 plays one generic cast montage regardless of spell; per-spell cast clips are out of scope here.
• New reflection helper PlaySlotMontageOnSkin; shared HumanEntity::IsCasting().