Smoke-sweep fixes: exact saves, local dates, safer remove, readable markers

- Garden and plant dialogs keep centimeters as the source of truth
  (LengthField in lib/units.ts): a no-change Save no longer rewrites
  900 cm as 899.922 or a 45 cm spacing as 44.958, bumping versions and
  writing bogus history entries on the way.
- The UI stamps every date with the browser's local day (lib/dates.ts).
  Journal notes already did; plop placement, fill and removal now do too,
  so a 9 pm placement isn't "planted tomorrow". The fill endpoint gained an
  optional plantedAt; API and agent callers still default to UTC today.
- Removing an object that holds plants asks first and says how many go
  with it. An empty one still goes straight away (one Undo restores it).
- The expanded plant card's action row wraps instead of clipping "Delete".
- Monogram lettering switches to a dark ink on pale marker colors (garlic,
  cabbage, marigold) instead of near-white on near-white.
- Copy-as-plan proposes the next free year and warns when the typed name
  already exists, so two gardens can't both read as "the 2027 plan".
- Plan cards show the base name with a "2027 plan" tag, so the year — the
  point of the name — survives truncation.
- A rejected model spec now says which model and why: a wrapped
  ErrInvalidInput's reason reaches the client as the 400's message, and the
  Settings field shows it inline instead of toasting "invalid input".

Also defuses a clock bomb in TestRemainingReturnsWhenAPlantingIsRemoved,
which only passed while the real date was before 2026-08-01.

Co-Authored-By: Claude Fable 5 <[email protected]>

internal/api/ops.go

@@ -55,6 +55,10 @@ type objectFillRequest struct {
 	// (individual plants in rows at true spacing). Empty = clump. An unknown value
 	// is refused by the service (#77).
 	Layout string `json:"layout"`
+	// PlantedAt dates every plop the fill makes (YYYY-MM-DD). The UI sends its
+	// local day; omitted, the server uses UTC today — which is tomorrow for an
+	// evening gardener west of Greenwich, so clients that know better say so.
+	PlantedAt *string `json:"plantedAt"`
 }
 
 func (h *handlers) fillObject(c *gin.Context) {
@@ -88,9 +92,9 @@ func (h *handlers) fillObject(c *gin.Context) {
 			return
 		}
 		region := service.Region{MinX: rect.MinX, MinY: rect.MinY, MaxX: rect.MaxX, MaxY: rect.MaxY}
-		created, err = h.svc.FillRegion(c.Request.Context(), actor, id, region, req.PlantID, req.SpacingOverrideCM, service.FillLayout(req.Layout))
+		created, err = h.svc.FillRegion(c.Request.Context(), actor, id, region, req.PlantID, req.SpacingOverrideCM, service.FillLayout(req.Layout), req.PlantedAt)
 	} else {
-		created, err = h.svc.FillNamedRegion(c.Request.Context(), actor, id, req.Region, req.PlantID, req.SpacingOverrideCM, service.FillLayout(req.Layout))
+		created, err = h.svc.FillNamedRegion(c.Request.Context(), actor, id, req.Region, req.PlantID, req.SpacingOverrideCM, service.FillLayout(req.Layout), req.PlantedAt)
 	}
 	if err != nil {
 		writeServiceError(c, err)