comfyui-json: address PR #85 review

Five issues raised by Copilot's review:

1. _resolve_benchmark_path's docstring/README claim that a set-but-
   broken BENCHMARK_JSON_PATH falls through to the well-known tier,
   but the implementation only handled "file missing". A path
   pointing at a directory or holding malformed JSON dropped
   straight to the SD1.5 fallback without consulting tier 3.
   Replaced with a true tiered try-and-load: walk
   (misc, env, well-known), attempt to load each, and fall through
   to the next on any failure (missing, not a regular file,
   unreadable, invalid JSON). The env-var case still surfaces a
   warning so a typo doesn't fail silently.

2. int(os.getenv("BENCHMARK_TEST_WIDTH", ...)) crashed on non-int
   values. Added _env_int helper that warns + returns default on
   ValueError. Empty string also handled.

3. random.choice([]) on an empty test_prompts.txt raised IndexError.
   _load_prompts now warns + uses a built-in _FALLBACK_PROMPT when
   the file is missing or yields no non-blank lines.

4. README already claimed "missing or unreadable" fall-through; the
   refactor in (1) makes the code match. No README change needed.

5. test_prompts.txt restored verbatim from the pre-rewrite tree
   carried real-person and IP-laden prompts (Pope Francis, Iron Man,
   Luke Skywalker, "Disney socialite"). Used automatically during
   warm-up they're a reputational/safety-filter risk for the worker.
   Replaced with generic equivalents that exercise the same workload
   characteristics (1 elderly figure on motorcycle, 1 armoured hero
   with axe, etc.).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

workers/comfyui-json/misc/test_prompts.txt

@@ -7,13 +7,13 @@ inspired by realflow-cinema4d editor features, create image of a transparent lux
 biker with backpack on his back riding a motorcycle, Style by Ade Santora, Oilpunk, Cover photo, craig mullins style, on the cover of a magazine, Outdoor Magazine, inspired by Alex Petruk APe, image of a male biker, Cover of an award-winning magazine, the man has a backpack, photo for magazine, with a backpack, magazine cover
 generate a collage-style illustration inspired by the Procreate raster graphic editor, photographic illustration with the theme, 2D vector, art for textile sublimation, containing surrealistic cartoon cat wearing a baseball cap and jeans standing in front of a poster, inspired by Sadao Watanabe, Doraemon, Japanese cartoon style, Eichiro Oda, Iconic high detail character, Director: Nakahara Nantenbō, Kastuhiro Otomo, image detailed, by Miyamoto, Hidetaka Miyazaki, Katsuhiro illustration, 8k, masterpiece, Minimize noise and grain in photo quality without lose quality and increase brightness and lighting,Symmetry and Alignment, Avoid asymmetrical shapes and out-of-focus points. Focus and Sharpness: Make sure the image is focused and sharp and encourages the viewer to see it as a work of art printed on fabric.
 fantasy medieval village world inside a glass sphere , high detail, fantasy, realistic, light effect, hyper detail, volumetric lighting, cinematic, macro, depth of field, blur, red light and clouds from the back, highly detailed epic cinematic concept art cg render made in maya, blender and photoshop, octane render, excellent composition, dynamic dramatic cinematic lighting, aesthetic, very inspirational, world inside a glass sphere by james gurney by artgerm with james jean, joe fenton and tristan eaton by ross tran, fine details
-Iron Man, (Arnold Tsang, Toru Nakayama), Masterpiece, Studio Quality, 6k , toa, toaair, 1boy, glowing, axe, mecha, science_fiction, solo, weapon, jungle , green_background, nature, outdoors, solo, tree, weapon, mask, dynamic lighting, detailed shading, digital texture painting
-(Pope Francis) wearing leather jacket is a DJ in a nightclub, mixing live on stage, giant mixing table, a masterpiece
-Pope Francis wearing biker (leather jacket), a masterpiece
-Luke Skywalker ordering a burger and fries from the Death Star canteen.
+armored hero with a glowing axe, mecha science_fiction, jungle background, dynamic lighting, detailed shading, digital texture painting, masterpiece, studio quality, 6k
+elderly figure in a leather jacket DJing in a smoky nightclub, mixing live on a giant console, dramatic stage lighting, a masterpiece
+elderly figure in a leather jacket on a motorcycle, magazine cover lighting, a masterpiece
+a young pilot ordering a burger and fries from a futuristic space cantina
 I want to generate a group avatar for a Feishu group chat. The role of this group is daily software technical communication. Now the subject technology stacks that members of this group discuss daily include: algorithms, data structures, optimization, functional programming, and the programming languages often discussed are: TypeScript, Java, python, etc. I hope this avatar has a simple aesthetic, this avatar is a single person avatar
 portrait Anime black girl cute-fine-face, pretty face, realistic shaded Perfect face, fine details. Anime. realistic shaded lighting by Ilya Kuvshinov Giuseppe Dangelico Pino and Michael Garmash and Rob Rey, IAMAG premiere, WLOP matte print, cute freckles, masterpiece
-young Disney socialite wearing a beige miniskirt, dark brown turtleneck sweater, small neckless, cute-fine-face, anime. illustration, realistic shaded perfect face, brown hair, grey eyes, fine details, realistic shaded lighting by ilya kuvshinov giuseppe dangelico pino and michael garmash and rob rey, iamag premiere, wlop matte print, a masterpiece
+young woman in modern fashion editorial, beige miniskirt and dark brown turtleneck sweater, soft studio lighting, brown hair, grey eyes, fine details, magazine cover style, a masterpiece
 Cute small cat sitting in a movie theater eating chicken wiggs watching a movie ,unreal engine, cozy indoor lighting, artstation, detailed, digital painting,cinematic,character design by mark ryden and pixar and hayao miyazaki, unreal 5, daz, hyperrealistic, octane render
 Cute small dog sitting in a movie theater eating popcorn watching a movie ,unreal engine, cozy indoor lighting, artstation, detailed, digital painting,cinematic,character design by mark ryden and pixar and hayao miyazaki, unreal 5, daz, hyperrealistic, octane render
 fox bracelet made of buckskin with fox features, rich details, fine carvings, studio lighting