feat: core schema redesign — dishes, structured recipes, cuisines, tags (iteration 7)

Replaces the flat JSONB-based recipe schema with a normalized relational model:

Schema (migrations consolidated to 001_initial_schema + 002_seed_data):
- New: dishes, dish_translations, dish_tags — canonical dish catalog
- New: cuisines, tags, dish_categories with _translations tables + full seed data
- New: recipe_ingredients, recipe_steps with _translations (replaces JSONB blobs)
- New: user_saved_recipes thin bookmark (drops saved_recipes + saved_recipe_translations)
- New: product_ingredients M2M table
- recipes: now a cooking variant of a dish (dish_id FK, no title/JSONB columns)
- recipe_translations: repurposed to per-language notes only
- products: mapping_id → primary_ingredient_id
- menu_items: recipe_id FK → recipes; adds dish_id
- meal_diary: adds dish_id, recipe_id → recipes, portion_g

Backend (Go):
- New packages: internal/cuisine, internal/tag, internal/dish (registry + handler + repo)
- New GET /cuisines, GET /tags (public), GET /dishes, GET /dishes/{id}, GET /recipes/{id}
- recipe, savedrecipe, menu, diary, product, ingredient packages updated for new schema

Flutter:
- New models: Cuisine, Tag; new providers: cuisineNamesProvider, tagNamesProvider
- recipe.dart: RecipeIngredient gains unit_code + effectiveUnit getter
- saved_recipe.dart: thin model, manual fromJson, computed nutrition getter
- diary_entry.dart: adds dishId, recipeId, portionG
- recipe_detail_screen.dart: localized cuisine/tag names via providers

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/internal/tag/handler.go

@@ -0,0 +1,28 @@
+package tag
+
+import (
+	"encoding/json"
+	"net/http"
+
+	"github.com/food-ai/backend/internal/locale"
+)
+
+type tagItem struct {
+	Slug string `json:"slug"`
+	Name string `json:"name"`
+}
+
+// List handles GET /tags — returns tags with names in the requested language.
+func List(w http.ResponseWriter, r *http.Request) {
+	lang := locale.FromContext(r.Context())
+	items := make([]tagItem, 0, len(Records))
+	for _, t := range Records {
+		name, ok := t.Translations[lang]
+		if !ok {
+			name = t.Name
+		}
+		items = append(items, tagItem{Slug: t.Slug, Name: name})
+	}
+	w.Header().Set("Content-Type", "application/json")
+	_ = json.NewEncoder(w).Encode(map[string]any{"tags": items})
+}

backend/internal/tag/registry.go

@@ -0,0 +1,79 @@
+package tag
+
+import (
+	"context"
+	"fmt"
+
+	"github.com/jackc/pgx/v5/pgxpool"
+)
+
+// Record is a tag loaded from DB with all its translations.
+type Record struct {
+	Slug         string
+	Name         string // English canonical name
+	SortOrder    int
+	Translations map[string]string // lang → localized name
+}
+
+// Records is the ordered list of tags, populated by LoadFromDB at startup.
+var Records []Record
+
+// LoadFromDB queries tags + tag_translations and populates Records.
+func LoadFromDB(ctx context.Context, pool *pgxpool.Pool) error {
+	rows, err := pool.Query(ctx, `
+		SELECT t.slug, t.name, t.sort_order, tt.lang, tt.name
+		FROM tags t
+		LEFT JOIN tag_translations tt ON tt.tag_slug = t.slug
+		ORDER BY t.sort_order, tt.lang`)
+	if err != nil {
+		return fmt.Errorf("load tags from db: %w", err)
+	}
+	defer rows.Close()
+
+	bySlug := map[string]*Record{}
+	var order []string
+	for rows.Next() {
+		var slug, engName string
+		var sortOrder int
+		var lang, name *string
+		if err := rows.Scan(&slug, &engName, &sortOrder, &lang, &name); err != nil {
+			return err
+		}
+		if _, ok := bySlug[slug]; !ok {
+			bySlug[slug] = &Record{
+				Slug:         slug,
+				Name:         engName,
+				SortOrder:    sortOrder,
+				Translations: map[string]string{},
+			}
+			order = append(order, slug)
+		}
+		if lang != nil && name != nil {
+			bySlug[slug].Translations[*lang] = *name
+		}
+	}
+	if err := rows.Err(); err != nil {
+		return err
+	}
+
+	result := make([]Record, 0, len(order))
+	for _, slug := range order {
+		result = append(result, *bySlug[slug])
+	}
+	Records = result
+	return nil
+}
+
+// NameFor returns the localized name for a tag slug.
+// Falls back to the English canonical name.
+func NameFor(slug, lang string) string {
+	for _, t := range Records {
+		if t.Slug == slug {
+			if name, ok := t.Translations[lang]; ok {
+				return name
+			}
+			return t.Name
+		}
+	}
+	return slug
+}