Agent: undo for real, past seasons, and tools that correct the record

Six tools the live assistant kept needing and a prompt that knows about them:

- undo_change wraps RevertChangeSet(source=agent). A revert is its own change
  set, so Run reports the last one as the turn's handle when the turn changed
  nothing else — an undo-only reply keeps its "Undo this", which is now a redo.
- describe_garden takes a year: the season view (GardenFull(year)), pulled
  plops included, with removed/removedAt per group and per plop; list_years
  says which years have records. Rotation questions finally have data.
- update_planting corrects a plop's date, count, label, radius or seed lot in
  place; remove_planting, remove_plantings and clear_object take a removedAt so
  a harvest can be backdated.
- update_journal_entry / delete_journal_entry correct a note instead of
  stacking a contradicting one.
- update_garden renames/resizes/re-units a garden and rewrites its notes — and
  the notes now go into the system prompt as the gardener's standing facts, so
  "remember we're in zone 6a" persists across conversations.

describe_garden also reports the garden's notes, version and grid, which the
new tools need. Prompt, CLAUDE.md and DESIGN.md updated to match; UI step
labels for the new tools.

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

internal/service/revisions_test.go

@@ -936,7 +936,7 @@ func TestRecordOutsideTheOpenScopeFilesUnderItsOwnGarden(t *testing.T) {
 	if _, conflicts, err := s.RevertChangeSet(ctx, owner, got.ID, domain.SourceUI); err != nil || len(conflicts) != 0 {
 		t.Fatalf("undo from B: err=%v conflicts=%+v", err, conflicts)
 	}
-	if d, err := s.DescribeGarden(ctx, owner, b.ID); err != nil || len(d.Objects) != 1 || d.Objects[0].Name != "Bed" {
+	if d, err := s.DescribeGarden(ctx, owner, b.ID, nil); err != nil || len(d.Objects) != 1 || d.Objects[0].Name != "Bed" {
 		t.Errorf("after undo B is %+v (%v), want the bed's name back", d, err)
 	}
 }