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>

mark.lua

@@ -0,0 +1,78 @@
+require "entity"
+
+-- A named destination on the grid. NPCs are sent to a Mark by name (see
+-- Npc:sendTo / World:markByName), so the name is the whole point of the object.
+--
+-- A Mark is a *debug non-collidable*: an editor-only annotation that everything
+-- passes through, shown only while the debug overlay is on. It is NOT a Note and
+-- shares no code with one — the two just happen to be siblings in that category.
+-- Its icon is a target, drawn procedurally so it needs no art asset.
+Mark = class("Mark", Entity)
+
+-- Entity only ever calls :getWidth/:getHeight on the sizing sprite (Mark:draw
+-- paints a target instead of blitting it), so a lightweight stub is enough and
+-- keeps Mark free of any borrowed artwork.
+local sizeStub = { getWidth = function() return 16 end, getHeight = function() return 16 end }
+
+-- The target is pixel art: a 16x16 bullseye (two rings + a centre dot) baked once
+-- into a list of on-pixels, drawn as blocky rectangles so it stays crisp at the
+-- game's nearest-neighbour scale instead of a smooth vector circle.
+local GRID = 16
+local targetPixels = {}
+do
+	local c = (GRID - 1) / 2   -- 7.5, the sub-pixel centre
+	for row = 0, GRID - 1 do
+		for col = 0, GRID - 1 do
+			local dist = math.sqrt((col - c) ^ 2 + (row - c) ^ 2)
+			local on = math.abs(dist - 6.5) < 0.7   -- outer ring
+				or math.abs(dist - 3.5) < 0.7        -- inner ring
+				or dist < 1.3                        -- centre dot
+			if on then targetPixels[#targetPixels + 1] = { col, row } end
+		end
+	end
+end
+
+function Mark:initialize(x, y, name)
+	self.markName = name or ""
+	self.saveClass = "mark"
+	-- programmatic marks are created from code on every room load, so they are
+	-- skipped by Room:serialize (see there) to avoid duplicating on disk.
+	self.programmatic = false
+	Entity.initialize(self, {
+		x = x, y = y,
+		color = "white",   -- representative only; Mark:draw is channel-agnostic
+		collision = "none",
+		sprite = sizeStub,
+	})
+end
+
+-- Drawn once (not per-channel) from the room's debug overlay pass, so it takes no
+-- channel argument. A faint pixel-art red target with its name beside it, kept at
+-- the same low opacity as a Note so it reads as an annotation, not a game object.
+function Mark:draw()
+	local p = self:getDrawPos()
+	love.graphics.setColor(1, 0.3, 0.25, 0.85)
+	for _, px in ipairs(targetPixels) do
+		love.graphics.rectangle("fill", p.x + px[1] * drawScale, p.y + px[2] * drawScale, drawScale, drawScale)
+	end
+	if self.markName ~= "" then
+		love.graphics.setColor(1, 0.5, 0.42, 0.85)
+		love.graphics.print(self.markName, p.x, p.y - 12)
+	end
+	love.graphics.setColor(1, 1, 1, 1)
+end
+
+-- The same pixel-art target baked into a 16x16 Image, for the editor toolbar
+-- button (full opacity there — it's a control, not a faint overlay). Cached, and
+-- built lazily so it only touches love.graphics once the editor needs it.
+function Mark.static.icon()
+	if Mark.static._icon then return Mark.static._icon end
+	local data = love.image.newImageData(GRID, GRID)
+	for _, px in ipairs(targetPixels) do
+		data:setPixel(px[1], px[2], 1, 0.3, 0.25, 1)
+	end
+	local img = love.graphics.newImage(data)
+	img:setFilter("nearest", "nearest")
+	Mark.static._icon = img
+	return img
+end