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>

tests/test_movement.lua

@@ -355,6 +355,12 @@ local function loadRoomClass()
 			end,
 		},
 	}
+	-- room pulls in note.lua/mark.lua, which call loadSprite at module-load time.
+	-- Provide a default stub so requiring room works; individual tests still
+	-- override loadSprite as needed.
+	loadSprite = loadSprite or function()
+		return {getWidth = function() return 16 end, getHeight = function() return 16 end}
+	end
 	require "room"
 end