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>

CLAUDE.md

@@ -15,10 +15,10 @@ lua tests/test_movement.lua  # run the pure matrix-movement tests
 
 `love` is not installed in this environment — you cannot run the game here; reason about the code statically.
 
-**LÖVE version matters.** The code targets the **0.10.x** API, not 11.x. Signals of this that you must preserve when editing:
-- Colors are `0–255` integers (`love.graphics.setColor(255, 255, 255)`), not `0–1` floats.
-- `sprite:getData()` / `img:getPixel` are used (see `sprite_manager.lua`); the 11.x replacements differ.
-Do not "modernize" these to the 11.x API unless explicitly asked — it would break the whole render/color path.
+**LÖVE version matters.** The code targets the **11.x** API — `conf.lua` pins `t.version = "11.5"`. Preserve these when editing:
+- Colors are normalized `0–1` floats (`love.graphics.setColor(1, 1, 1)`), not `0–255` integers — see `color.lua`.
+- Pixel inspection uses the 11.x ImageData API: `love.image.newImageData(path)` + `ImageData:getPixel` (see `getCellsFromSprite` in `_helpers.lua`). `Image:getData()` was removed in 11 — don't reintroduce it.
+Do not "downgrade" these to the 0.10.x API — it would break the whole render/color path.
 
 ## The core mechanic (read this before touching gameplay code)
 
@@ -36,7 +36,7 @@ The player is not one entity — it is **up to three simultaneous colored copies
 - `entity.lua` — `Entity` base class (middleclass). Everything on the grid subclasses it: `Player`, `Box`, `Wall`, `Switch`, `Door`, `Artifact`, `Art`, `Ass` (assorted decor), `npc`. Grid↔pixel conversion, occupied-cell shapes, and the `sha()` jitter all live here.
 - `room.lua` — the orchestrator: entity registries, per-color matrices, movement/push/pull, tick, switch/door logic, room transitions (`nextRoom`), and serialization.
 - `color.lua` — `Color` class + the canonical RGB(W) table. `gColor` globals are created in `main._initGlobalColors`.
-- `sprite_manager.lua` — loads all images into the `sprites` global and precomputes `spriteCells` (which 16×16 cells of a sprite are non-empty, for multi-cell collision shapes). Sprites are `16px`-per-cell.
+- Sprite loading: `loadSprite(path)` in `_helpers.lua` returns a cached `Image`. Per-asset occupied-cell shapes (which 16×16 cells are non-empty, for multi-cell collision) are precomputed by `getCellsFromSprite` (`_helpers.lua`) and gathered into `globalAssetProperties` by `getAllAssets` (`level_editor/object_attributes.lua`). Sprites are `16px`-per-cell. (An older `sprite_manager.lua` that populated `sprites`/`spriteCells` globals is gone; the stray `sprites.*` / `spriteCells[...]` references in stub files like `artifact.lua` / `assorted.lua` are vestigial.)
 - `input.lua`, `shaders.lua` (`wiggle`, `glow` GLSL), `_helpers.lua` (`lerp`/`map`/`constrain`), `_debug_helpers.lua` (`printMatrix`, `shallowTablePrint`, `randomPosition`).
 - `dialogue_manager.lua` is currently empty; `npc.lua`/`art.lua`/`artifact.lua` are stubs or reference art folders not present in `art/`.