Detect bleeds authoritatively via Spell.dbc mechanics

Add a GetSpellSchool bleed check (Priority 0.5) backed by DBC SpellMechanic
data instead of damage-event learning / name patterns:
- GetSpellMechanicByID == 15 catches spell-level bleeds (Garrote, Rupture,
  Rend, Rip, Pounce, Deep Wounds).
- New ClassicAPI GetSpellEffectMechanics catches effect-level bleeds that the
  spell-level field misses -- Rake is spell-level 0 with EffectMechanic[2]=15.

Wrap C_Spell.GetSpellEffectMechanics in ClassicAPI.lua (nil-guarded so older
builds fall back to spell-level only). Verified against the client Spell.dbc.

Also drop Hemorrhage from the bleed name-pattern fallback: the DBC gives it no
bleed mechanic (physical damage), so bleed-immune mobs don't resist it -- it was
a false positive. Existing learning / split-damage / patterns remain as fallback.

ClassicAPI.lua

@@ -168,6 +168,19 @@ function API.GetSpellMechanicByID(spellID)
     return C_Spell.GetSpellMechanicByID(spellID)
 end
 
+-- Per-effect SpellMechanic ids (Spell.dbc EffectMechanic[3]) as {m1, m2, m3},
+-- or nil for an invalid spell / 0 for an effect with no mechanic. Complements
+-- GetSpellMechanicByID, which only reads the spell-level Mechanic field: vanilla
+-- stores some mechanics on an effect instead (e.g. Rake's bleed is effect-level,
+-- so GetSpellMechanicByID returns 0 but this returns {0,15,0}). Nil-guarded so an
+-- older ClassicAPI build without the function degrades gracefully.
+function API.GetSpellEffectMechanics(spellID)
+    if type(C_Spell.GetSpellEffectMechanics) == "function" then
+        return C_Spell.GetSpellEffectMechanics(spellID)
+    end
+    return nil
+end
+
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 -- State
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