Generate the week's Supply run from its plan

Add internal/shopping with Generate(weekStart), one entry point for the
first generation and every regeneration. It builds one group per plan
day (dinner_id, date, position by date) and one item per ingredient of
the dinner's recipe, in ingredient order, reusing the values recipe
grounding stored: a fetched recipe's normalized name with qty and unit
joined for display, or a manual recipe's line as typed with no qty. A
day whose dinner has no recipe or no ingredients gets no group and is
reported in Skipped. Regenerating keeps the id and needed flag of each
item whose (dinner_id, name) is unchanged, matching repeated names in
order; new items are needed and items no longer planned are removed. It
is deterministic and makes no model call. A frozen list is refused.

Migration 0016 makes shopping_lists.title nullable (never empty) so a
list exists untitled until the AI titles it, and adds shopping_groups.date.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/dinners/grounding.go

@@ -68,6 +68,13 @@ const (
 	manualSourcePrefix = "mealquest:manual:"
 )
 
+// IsManualRecipe reports whether sourceURL, a recipes.source_url, is that
+// of a recipe entered by hand. Its ingredients are stored as typed, in
+// raw_text only: no model normalizes them, so name, qty and unit are NULL.
+func IsManualRecipe(sourceURL string) bool {
+	return strings.HasPrefix(sourceURL, manualSourcePrefix)
+}
+
 // GroundTimeout bounds grounding a candidate or link by hand, which runs in
 // the request: the page fetch (recipes.Timeout), its photo download and
 // normalize_recipe (harness.DefaultTimeout), with some slack.