Backend Phase C: Sync-Kern + Caddy behind-proxy

Sync-Kern:
- internal/sync/hlc.go: Hybrid Logical Clock (wall_ms<<16|counter)
  Tick/Now/After, global mutex, strikt monoton + kausal korrekt
- internal/sync/hlc_test.go: Unit-Tests (monoton, kausal, keine Duplikate)

Store-Schicht:
- internal/store/opstore.go: AppendOps idempotent via UNIQUE(client_id,
  client_seq) ON CONFLICT DO NOTHING; LWW-Projektion (list_create/
  rename/delete, item_add/update/remove) in derselben Transaktion;
  PullOps mit Cursor (seq > since, 500er Pages)
- internal/store/liststore.go: CreateList / GetLists / GetList
- internal/store/itemstore.go: GetItems (nicht-gelöschte Items)
- internal/store/suggeststore.go: Search (pg_trgm + LIKE-fallback, 10)

HTTP-Handler:
- internal/httpapi/lists.go: GET/POST /api/lists, GET /api/lists/{id}
- internal/httpapi/ops.go: POST /api/lists/{id}/ops (Push),
  GET /api/lists/{id}/ops (Pull ?since=)
- internal/httpapi/suggest.go: GET /api/suggestions?q=
- internal/httpapi/api.go: alle Routen verdrahtet (RequireAuth)

Deployment:
- deploy/Caddyfile.behind-proxy: auto_https off, trusted_proxies
- deploy/Caddyfile: X-Forwarded-Proto hinzugefügt, Kommentar aktualisiert
- deploy/docker-compose.yml: CADDY_HTTP_PORT + CADDY_HTTPS_PORT
- deploy/.env.example: Caddy-Port-Variablen dokumentiert

go build ./... && go vet ./... && go test ./... ✅
HLC-Tests: monoton, kausal, keine Duplikate ✅
AGENTS.md: Phase C vollständig ✅

backend/internal/store/itemstore.go

@@ -0,0 +1,64 @@
+package store
+
+import (
+	"context"
+	"fmt"
+	"time"
+
+	"github.com/google/uuid"
+	"github.com/jackc/pgx/v5/pgxpool"
+)
+
+// Item is the projection of an items row.
+type Item struct {
+	ID        uuid.UUID  `json:"id"`
+	ListID    uuid.UUID  `json:"list_id"`
+	Name      string     `json:"name"`
+	Quantity  *string    `json:"quantity,omitempty"`
+	Checked   bool       `json:"checked"`
+	SortOrder *int       `json:"sort_order,omitempty"`
+	CreatedAt time.Time  `json:"created_at"`
+	UpdatedAt time.Time  `json:"updated_at"`
+	DeletedAt *time.Time `json:"deleted_at,omitempty"`
+	HLCTS     int64      `json:"hlc_ts"`
+	ClientID  *uuid.UUID `json:"client_id,omitempty"`
+	CheckedAt *time.Time `json:"checked_at,omitempty"`
+}
+
+// ItemStore provides read access to the items projection.
+type ItemStore struct {
+	pool *pgxpool.Pool
+}
+
+// NewItemStore creates an ItemStore backed by the given pool.
+func NewItemStore(pool *pgxpool.Pool) *ItemStore { return &ItemStore{pool: pool} }
+
+// GetItems returns all non-deleted items for listID, ordered by sort_order then creation time.
+func (s *ItemStore) GetItems(ctx context.Context, listID uuid.UUID) ([]Item, error) {
+	rows, err := s.pool.Query(ctx, `
+		SELECT id, list_id, name, quantity, checked, sort_order,
+		       created_at, updated_at, hlc_ts, client_id, checked_at
+		FROM items
+		WHERE list_id = $1 AND deleted_at IS NULL
+		ORDER BY sort_order ASC NULLS LAST, created_at ASC`,
+		listID,
+	)
+	if err != nil {
+		return nil, fmt.Errorf("itemstore: get items: %w", err)
+	}
+	defer rows.Close()
+
+	var items []Item
+	for rows.Next() {
+		var it Item
+		if err := rows.Scan(
+			&it.ID, &it.ListID, &it.Name, &it.Quantity, &it.Checked,
+			&it.SortOrder, &it.CreatedAt, &it.UpdatedAt,
+			&it.HLCTS, &it.ClientID, &it.CheckedAt,
+		); err != nil {
+			return nil, fmt.Errorf("itemstore: scan item row: %w", err)
+		}
+		items = append(items, it)
+	}
+	return items, rows.Err()
+}