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/offsets.zig

@@ -42,6 +42,12 @@ pub const DESC_ENTRY: usize = 0x03 * 4;
 /// UNIT_NPC_FLAGS = OBJECT_END(0x06) + 0x8D = 0x93
 pub const DESC_NPC_FLAGS: usize = 0x93 * 4;
 
+/// UNIT_DYNAMIC_FLAGS = OBJECT_END(0x06) + 0x90 = 0x96
+pub const DESC_UNIT_DYNAMIC_FLAGS: usize = 0x96 * 4;
+
+/// Bit 0: unit corpse is lootable by the local player.
+pub const UNIT_DYNFLAG_LOOTABLE: u32 = 0x01;
+
 /// GAMEOBJECT_TYPE_ID (index 0x15)
 pub const DESC_GO_TYPE: usize = 0x15 * 4;