docs(recipes): document isRecipe-flag behavior in get_recipe_box (v0.11.8)

Documentation-only release explaining the isRecipe flag:
- isRecipe='true': Real recipes in the recipe box
- isRecipe='false': Free-text stubs from meal planner OR old imported recipes
  never properly tagged (e.g. recipe/16282169_7055369 'Elsässer Flammkuchen')

get_recipe_box filters strictly on isRecipe='true' — consistent with Family Wall app.

Updated SPEC.md, README.md, CLAUDE.md with v0.11.8.

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

.gitignore

@@ -48,3 +48,4 @@ probe_*.py
 probe_*.txt
 p*_err.txt
 test_*.py
+reference/