[paultristanwagner]

All code in this PR was written by an AI agent (Claude Opus 5.5) working with me; I directed it and tested the results on my own account. Feel free to take, change or drop any part of it.

Part of #73.

Adds an update_recipe tool to edit a recipe in place: rename it, change
its ingredients or amounts, resize its serving, or change its notes.
update_custom_food refuses recipes, because their nutrients come from
the ingredients.

The app edits a recipe the same way update_custom_food edits a food: it
re-sends the whole object to POST /api/v2/add_food with its id. It recalculates the per-100 g
nutrients itself before sending; the server stores what it gets. Verified
against the live API with throwaway recipes:

• new ingredients replace the old list (they get new ingredient ids)
• measures keep their ids
• the translation's name follows name
• the server refuses a save that drops the g measure
  ("Cannot remove the grams measure from a gram-based food")

Changes:

• client: the ingredient resolution and nutrient math in
  create_recipe moved into _recipe_ingredients without changes, so both
  methods share it. update_recipe(food_id, *, name, ingredients, serving_grams, comments) edits under the per-food lock:
  • the "full recipe" measure follows the new batch weight
  • a default serving that was the whole batch stays the whole batch
  • any other serving keeps its weight unless serving_grams is given
  • saved meals are refused, because their measures are serving-based
• server: update_recipe tool. add_recipe's ingredient parsing moved
  into _parse_ingredients, which both tools use. get_food_details now
  returns a recipe's ingredients, in the shape these tools take, so they
  can be read before editing.
• README: tool table row.

https://claude.ai/code/session_01MCJFDo71qoSqTRtcGfkpXJ