Add named Marks and cross-room NPC pathfinding

- Mark: a debug non-collidable named destination (pixel-art target icon),
  editor tool + name modal, globally-unique names, programmatic Room:addMark
- NPCs walk to Marks: each RGB copy is a per-room resident (like the player),
  running its own A* on its own colour layer, transferring rooms as it crosses
  seams; rendered and collided by the room it currently stands in
- Player copies are obstacles in NPC pathfinding
- A* is footprint-aware for multi-cell NPCs
- Editor: click an NPC to open a filterable destination picker
- Ink: Dialogue.open binds walk_to; Jorge can be sent to "end"/"begin"
- Fix: a blocked NPC now replans each tick and resumes instead of freezing
- [npc] move diagnostics under DEBUG (start/goal/route or block reason)
- Docs (adding-npcs) + CLAUDE.md LÖVE 11.x/float-colour corrections
- Fix test harness loadSprite stub; movement tests green (28)

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

dialogable.lua

@@ -8,8 +8,20 @@ Dialogable = {}
 function Dialogable:onBump()
 	if self.book then
 		local wasOpen = Dialogue.isOpen()
-		Dialogue.open(self.book)
+		Dialogue.open(self.book, self:dialogueBindings())
 		if Sound and not wasOpen then Sound.jabber() end
 	end
 	return true
 end
+
+-- Ink external functions exposed to this talker's book. A walking NPC (one that
+-- includes Walker) can be sent to a named Mark with `~ walk_to("mark_name")`,
+-- e.g. to leave after a conversation.
+function Dialogable:dialogueBindings()
+	local talker = self
+	return {
+		walk_to = function(markName)
+			if talker.sendTo then talker:sendTo(markName) end
+		end,
+	}
+end