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]>

web/src/lib/units.ts

@@ -227,3 +227,45 @@ export function formatLength(cm: number, unit: UnitPref): string {
 export function formatSize(widthCm: number, heightCm: number, unit: UnitPref): string {
   return `${formatLength(widthCm, unit)} × ${formatLength(heightCm, unit)}`
 }
+
+// --- Typed-length fields ----------------------------------------------------
+// A dialog field that takes a length holds TWO things: the text the person sees
+// and the centimeters it means. The centimeters change only when the person
+// types; re-showing the field in another unit, or saving without touching it,
+// reuses them as they are. Parsing the displayed text back on save is how a
+// no-change Save once turned 900 cm into 899.922 — "29′ 6.3″" is the nearest
+// tenth of an inch, not the number that was loaded.
+
+/** A length as typed and as stored; `cm` is null while the text doesn't parse. */
+export interface LengthField {
+  text: string
+  cm: number | null
+}
+
+/** A dimension field (meters, or feet and inches) showing `cm`. */
+export function dimensionField(cm: number, unit: UnitPref): LengthField {
+  return { text: formatDimensionInput(cm, unit), cm }
+}
+
+/** The person typed `text` into a dimension field. */
+export function editDimensionField(text: string, unit: UnitPref): LengthField {
+  return { text, cm: parseDimension(text, unit) }
+}
+
+/** Re-show a dimension field in another unit; the centimeters don't move. A
+ *  field that doesn't parse keeps its text, so the typo stays visible. */
+export function convertDimensionField(field: LengthField, unit: UnitPref): LengthField {
+  return field.cm === null ? field : dimensionField(field.cm, unit)
+}
+
+/** A spacing field (cm, or inches) showing `cm`. */
+export function spacingField(cm: number, unit: UnitPref): LengthField {
+  return { text: String(spacingFromCm(cm, unit)), cm }
+}
+
+/** The person typed `text` into a spacing field. */
+export function editSpacingField(text: string, unit: UnitPref): LengthField {
+  const trimmed = text.trim()
+  const n = Number(trimmed)
+  return { text, cm: trimmed !== '' && Number.isFinite(n) ? cmFromSpacing(n, unit) : null }
+}