feat: chatbot model setting + tool-calling toggle, simplify admin AI config (v0.59.0)

Chatbot (general assistant + per-recipe Q&A) now resolves its default model
from its own site setting (DEFAULT_CHAT_PROVIDER/MODEL) instead of sharing
the generic "text" use case with recipe generation, so admins can point it
at a different model.

Added AI_TOOL_CALLING_ENABLED: turns off the chatbot's createRecipe/
addToShoppingList tools (and the forced-retry pass) for models that don't
reliably support tool calling — it falls back to plain text answers.

Simplified the admin AI Configuration page: it showed provider keys and
routing settings twice (a read-only card, then an identical edit form).
Merged into one editable section; the resolved fallback provider is now a
one-line note instead of its own card.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

apps/web/lib/site-settings.ts

@@ -16,6 +16,9 @@ export type SiteSettingKey =
   | "DEFAULT_VISION_MODEL"
   | "DEFAULT_MEAL_PLAN_PROVIDER"
   | "DEFAULT_MEAL_PLAN_MODEL"
+  | "DEFAULT_CHAT_PROVIDER"
+  | "DEFAULT_CHAT_MODEL"
+  | "AI_TOOL_CALLING_ENABLED"
   | "GITEA_URL"
   | "GITEA_TOKEN"
   | "GITEA_REPO";
@@ -62,6 +65,9 @@ export async function getAllSiteSettings(): Promise<Record<string, { value: stri
     "DEFAULT_VISION_MODEL",
     "DEFAULT_MEAL_PLAN_PROVIDER",
     "DEFAULT_MEAL_PLAN_MODEL",
+    "DEFAULT_CHAT_PROVIDER",
+    "DEFAULT_CHAT_MODEL",
+    "AI_TOOL_CALLING_ENABLED",
     "GITEA_URL",
     "GITEA_TOKEN",
     "GITEA_REPO",
@@ -93,6 +99,13 @@ export async function isSignupsDisabled(): Promise<boolean> {
   return (await getSiteSetting("SIGNUPS_DISABLED")) === "true";
 }
 
+/** Defaults to enabled — the chatbot's createRecipe/addToShoppingList tools
+ * only get turned off explicitly, e.g. for a local model that can't reliably
+ * call tools. */
+export async function isAiToolCallingEnabled(): Promise<boolean> {
+  return (await getSiteSetting("AI_TOOL_CALLING_ENABLED")) !== "false";
+}
+
 export async function setSiteSetting(
   key: SiteSettingKey,
   value: string | null,