feat: cooking assistant can propose creating a recipe

Gives the general chat a createRecipe tool (Vercel AI SDK, stepCountIs(3))
scoped so it can only ever produce a draft — the tool's execute is a pure
echo, no DB write. The route surfaces the tool call as proposedRecipe
alongside the normal text answer; the chat UI renders it as a card with
explicit Create/Discard buttons. Create POSTs to the existing
/api/v1/recipes endpoint — the same code path and tier/recipe-count limit
the manual editor already goes through — so there's exactly one place
that actually creates a recipe row, and nothing happens without the user
clicking Create.

Scoped to the general assistant only (not per-recipe chat), and to one
tool for now — addToShoppingList/generateMealPlan are follow-ups.

v0.45.0

apps/web/messages/en.json

@@ -459,7 +459,13 @@
     "subtitle": "Ask any cooking question — not tied to a specific recipe",
     "intro": "Ask anything about cooking — techniques, substitutions, timing, equipment…",
     "inputPlaceholder": "Ask a question…",
-    "send": "Send message"
+    "send": "Send message",
+    "proposalSummary": "{ingredients} ingredients · {steps} steps",
+    "proposalCreateButton": "Create recipe",
+    "proposalDiscardButton": "Discard",
+    "proposalCreated": "Recipe created — opening editor…",
+    "proposalDiscarded": "Discarded",
+    "proposalCreateFailed": "Failed to create recipe"
   },
   "conversations": {
     "menuAriaLabel": "Conversations",