refactor: migrate DI to Wire, replace startup registries with on-demand DB queries

- Add google/wire; generate wire_gen.go from wire.go injector
- Move all constructor wiring out of main.go into providers.go / wire.go
- Export recognition.IngredientRepository (was unexported, blocked Wire binding)
- Delete units/cuisine/tag registry.go files (global state + unused NameFor helpers)
- Replace List handlers with NewListHandler(pool) using COALESCE SQL queries
- Remove units/cuisine/tag LoadFromDB from server startup; locale.LoadFromDB kept
  (locale.Supported is used by language middleware on every request)

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

backend/internal/units/handler.go

@@ -2,9 +2,11 @@ package units
 
 import (
 	"encoding/json"
+	"log/slog"
 	"net/http"
 
 	"github.com/food-ai/backend/internal/locale"
+	"github.com/jackc/pgx/v5/pgxpool"
 )
 
 type unitItem struct {
@@ -12,17 +14,47 @@ type unitItem struct {
 	Name string `json:"name"`
 }
 
-// List handles GET /units — returns units with names in the requested language.
-func List(w http.ResponseWriter, r *http.Request) {
-	lang := locale.FromContext(r.Context())
-	items := make([]unitItem, 0, len(Records))
-	for _, u := range Records {
-		name, ok := u.Translations[lang]
-		if !ok {
-			name = u.Code // fallback to English code
+// NewListHandler returns an http.HandlerFunc for GET /units.
+// It queries the database directly, resolving translations via COALESCE.
+func NewListHandler(pool *pgxpool.Pool) http.HandlerFunc {
+	return func(responseWriter http.ResponseWriter, request *http.Request) {
+		lang := locale.FromContext(request.Context())
+
+		rows, queryError := pool.Query(request.Context(), `
+			SELECT u.code, COALESCE(ut.name, u.code) AS name
+			FROM units u
+			LEFT JOIN unit_translations ut ON ut.unit_code = u.code AND ut.lang = $1
+			ORDER BY u.sort_order`, lang)
+		if queryError != nil {
+			slog.Error("list units", "err", queryError)
+			writeErrorJSON(responseWriter, http.StatusInternalServerError, "failed to load units")
+			return
 		}
-		items = append(items, unitItem{Code: u.Code, Name: name})
+		defer rows.Close()
+
+		items := make([]unitItem, 0)
+		for rows.Next() {
+			var item unitItem
+			if scanError := rows.Scan(&item.Code, &item.Name); scanError != nil {
+				slog.Error("scan unit row", "err", scanError)
+				writeErrorJSON(responseWriter, http.StatusInternalServerError, "failed to load units")
+				return
+			}
+			items = append(items, item)
+		}
+		if rowsError := rows.Err(); rowsError != nil {
+			slog.Error("iterate unit rows", "err", rowsError)
+			writeErrorJSON(responseWriter, http.StatusInternalServerError, "failed to load units")
+			return
+		}
+
+		responseWriter.Header().Set("Content-Type", "application/json")
+		_ = json.NewEncoder(responseWriter).Encode(map[string]any{"units": items})
 	}
-	w.Header().Set("Content-Type", "application/json")
-	_ = json.NewEncoder(w).Encode(map[string]any{"units": items})
+}
+
+func writeErrorJSON(responseWriter http.ResponseWriter, status int, message string) {
+	responseWriter.Header().Set("Content-Type", "application/json")
+	responseWriter.WriteHeader(status)
+	_ = json.NewEncoder(responseWriter).Encode(map[string]string{"error": message})
 }

backend/internal/units/registry.go

@@ -1,73 +0,0 @@
-package units
-
-import (
-	"context"
-	"fmt"
-
-	"github.com/jackc/pgx/v5/pgxpool"
-)
-
-// Record is a unit loaded from DB with all its translations.
-type Record struct {
-	Code         string
-	SortOrder    int
-	Translations map[string]string // lang → localized name
-}
-
-// Records is the ordered list of active units, populated by LoadFromDB at startup.
-var Records []Record
-
-// LoadFromDB queries units + unit_translations and populates Records.
-func LoadFromDB(ctx context.Context, pool *pgxpool.Pool) error {
-	rows, err := pool.Query(ctx, `
-		SELECT u.code, u.sort_order, ut.lang, ut.name
-		FROM units u
-		LEFT JOIN unit_translations ut ON ut.unit_code = u.code
-		ORDER BY u.sort_order, ut.lang`)
-	if err != nil {
-		return fmt.Errorf("load units from db: %w", err)
-	}
-	defer rows.Close()
-
-	byCode := map[string]*Record{}
-	var order []string
-	for rows.Next() {
-		var code string
-		var sortOrder int
-		var lang, name *string
-		if err := rows.Scan(&code, &sortOrder, &lang, &name); err != nil {
-			return err
-		}
-		if _, ok := byCode[code]; !ok {
-			byCode[code] = &Record{Code: code, SortOrder: sortOrder, Translations: map[string]string{}}
-			order = append(order, code)
-		}
-		if lang != nil && name != nil {
-			byCode[code].Translations[*lang] = *name
-		}
-	}
-	if err := rows.Err(); err != nil {
-		return err
-	}
-
-	result := make([]Record, 0, len(order))
-	for _, code := range order {
-		result = append(result, *byCode[code])
-	}
-	Records = result
-	return nil
-}
-
-// NameFor returns the localized name for a unit code.
-// Falls back to the code itself when no translation exists.
-func NameFor(code, lang string) string {
-	for _, u := range Records {
-		if u.Code == code {
-			if name, ok := u.Translations[lang]; ok {
-				return name
-			}
-			return u.Code
-		}
-	}
-	return code
-}