Address Gadfly review on the garden copy

* api: detect an absent copy body by io.EOF from the decoder rather than
  Content-Length. A chunked request reports -1, not 0, so the length test
  read an empty chunked body as malformed and 400'd instead of taking the
  default-name path. Covered by a new unknown-length test.

* store: hoist the garden_objects/plantings INSERTs into shared
  objectInsert/plantingInsert statements with matching *InsertArgs
  helpers. CopyGarden had its own copies of both column lists, so a
  column added to the table could be wired into Create* and silently
  dropped from a copy.

* store: move the queryer interface to sqlite.go, next to the other
  shared query plumbing, instead of users.go.

* web: derive a copy's prefilled name via defaultCopyName, mirroring the
  server's copyName including its 200-BYTE cap. The inline
  `${name} (copy)` both duplicated the suffix and, for a garden whose
  name was already at the cap, prefilled an over-long name that the
  server rejected with a 400. Unit-tested, including multi-byte
  truncation on a code-point boundary.

* test: drop a throwaway `_ = kept`.

Co-Authored-By: Claude Opus 4.8 (1M context) <[email protected]>

internal/api/gardens_test.go

@@ -2,8 +2,11 @@ package api
 
 import (
 	"encoding/json"
+	"io"
 	"net/http"
+	"net/http/httptest"
 	"strconv"
+	"strings"
 	"testing"
 
 	"github.com/gin-gonic/gin"
@@ -247,3 +250,32 @@ func TestCopyGardenEndpoint(t *testing.T) {
 		t.Errorf("bad body status = %d, want 400", w.Code)
 	}
 }
+
+// A body of unknown length (chunked transfer, Content-Length -1) that turns out
+// to be empty must take the default-name path, not fail as malformed.
+func TestCopyGardenEmptyChunkedBody(t *testing.T) {
+	r := authEngine(t, localCfg())
+	cookie := registerAndCookie(t, r, "[email protected]")
+
+	w := doJSON(t, r, http.MethodPost, "/api/v1/gardens", map[string]any{"name": "Home"}, cookie)
+	id := int64(decodeMap(t, w.Body.Bytes())["id"].(float64))
+
+	// A plain io.Reader (not a *strings.Reader/*bytes.Buffer) leaves
+	// ContentLength at -1, which is what a chunked request looks like server-side.
+	req := httptest.NewRequest(http.MethodPost,
+		"/api/v1/gardens/"+strconv.FormatInt(id, 10)+"/copy", io.NopCloser(strings.NewReader("")))
+	req.Header.Set("Content-Type", "application/json")
+	req.AddCookie(cookie)
+	if req.ContentLength != -1 {
+		t.Fatalf("test setup: ContentLength = %d, want -1 (unknown)", req.ContentLength)
+	}
+	rec := httptest.NewRecorder()
+	r.ServeHTTP(rec, req)
+
+	if rec.Code != http.StatusCreated {
+		t.Fatalf("status = %d, want 201; body %s", rec.Code, rec.Body.String())
+	}
+	if got := decodeMap(t, rec.Body.Bytes())["name"]; got != "Home (copy)" {
+		t.Errorf("name = %v, want the derived 'Home (copy)'", got)
+	}
+}