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/service/instance_settings.go

@@ -2,6 +2,8 @@ package service
 
 import (
 	"context"
+	"errors"
+	"fmt"
 	"strings"
 
 	"gitea.stevedudenhoeffer.com/steve/pansy/internal/agentmodel"
@@ -61,12 +63,15 @@ func (s *Service) UpdateInstanceSettings(ctx context.Context, actorID int64, pat
 	model := strings.TrimSpace(patch.AgentModel)
 	vision := strings.TrimSpace(patch.VisionModel)
 	// Validate non-empty specs up front. An empty one is the "inherit env"
-	// sentinel and needs no check — the env value was validated at boot.
-	for _, spec := range []string{model, vision} {
-		if spec != "" {
-			if err := agentmodel.Validate(s.cfg.Agent.OllamaCloudAPIKey, spec); err != nil {
-				return nil, domain.ErrInvalidInput
-			}
+	// sentinel and needs no check — the env value was validated at boot. The
+	// reason rides on the sentinel so the 400 can show it: "unknown provider"
+	// is something a person can act on, "invalid input" is not.
+	for _, f := range []struct{ label, spec string }{{"chat model", model}, {"vision model", vision}} {
+		if f.spec == "" {
+			continue
+		}
+		if err := agentmodel.Validate(s.cfg.Agent.OllamaCloudAPIKey, f.spec); err != nil {
+			return nil, fmt.Errorf("%w: %s %q: %v", domain.ErrInvalidInput, f.label, f.spec, specReason(err))
 		}
 	}
 	return s.store.UpdateInstanceSettings(ctx, &domain.InstanceSettings{
@@ -166,3 +171,12 @@ func (s *Service) EffectiveConfig(ctx context.Context) (EffectiveAgent, Effectiv
 	}
 	return s.agentOver(st), s.visionOver(st), nil
 }
+
+// specReason strips agentmodel's own "resolve %q:" wrapping so the message
+// reads "unknown provider …" rather than repeating the spec twice.
+func specReason(err error) string {
+	if u := errors.Unwrap(err); u != nil {
+		return u.Error()
+	}
+	return err.Error()
+}