Clickthrough: lootable corpses prioritize over players

Lootable unit corpses (UNIT_DYNFLAG_LOOTABLE) now click-through over
blocking players, matching the existing behavior for interactable NPCs
and game objects. Adds isLootable() check to the interactable NPC test
and UNIT_DYNAMIC_FLAGS descriptor offset to shared offsets.

Also adds RELEASE_NOTES.md for tracking changes between releases, and
adds a checklist item in RELEASING.md to review it before publishing.

src/wow.zig

@@ -122,6 +122,12 @@ pub fn getNpcFlags(obj: u32) u32 {
     return hook.readMem(u32, desc + o.DESC_NPC_FLAGS);
 }
 
+pub fn isLootable(obj: u32) bool {
+    const desc = getDescriptor(obj);
+    if (!isValidPtr(desc)) return 0 != 0;
+    return (hook.readMem(u32, desc + o.DESC_UNIT_DYNAMIC_FLAGS) & o.UNIT_DYNFLAG_LOOTABLE) != 0;
+}
+
 // =============================================================================
 // Unit helpers
 // =============================================================================