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/plan.ts

@@ -40,3 +40,17 @@ export function planGardensOf<G extends { id: number; name: string }>(base: stri
   }
   return out.sort((a, b) => a.year - b.year)
 }
+
+/** The first year from `from` on that `base` has no plan copy for among
+ *  `names`, so a new copy never proposes a name that is already taken — two
+ *  "Back Yard — 2027"s would both be offered as the 2027 plan. */
+export function nextPlanYear(base: string, names: readonly string[], from: number): number {
+  const taken = new Set<number>()
+  for (const n of names) {
+    const p = parsePlanName(n)
+    if (p && p.base === base.trim()) taken.add(p.year)
+  }
+  let year = from
+  while (taken.has(year)) year += 1
+  return year
+}