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.go

@@ -2,6 +2,7 @@ package api
 
 import (
 	"errors"
+	"io"
 	"net/http"
 
 	"github.com/gin-gonic/gin"
@@ -115,13 +116,13 @@ func (h *handlers) copyGarden(c *gin.Context) {
 		return
 	}
 	// The body is optional — POST with no body means "copy under the default
-	// name" — so only decode when one was actually sent.
+	// name". An absent body surfaces as io.EOF from the decoder, which is the
+	// reliable signal: Content-Length is -1 (not 0) for a chunked request, so
+	// testing the length would misread an empty chunked body as malformed.
 	var req gardenCopyRequest
-	if c.Request.ContentLength != 0 {
-		if err := c.ShouldBindJSON(&req); err != nil {
-			writeAPIError(c, http.StatusBadRequest, "INVALID_INPUT", "name must be a string")
-			return
-		}
+	if err := c.ShouldBindJSON(&req); err != nil && !errors.Is(err, io.EOF) {
+		writeAPIError(c, http.StatusBadRequest, "INVALID_INPUT", "name must be a string")
+		return
 	}
 	g, err := h.svc.CopyGarden(c.Request.Context(), mustActor(c).ID, id, req.Name)
 	if err != nil {