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.test.ts

@@ -1,5 +1,5 @@
 import { describe, expect, it } from 'vitest'
-import { parsePlanName, planGardensOf, planNameFor, planYearOf } from './plan'
+import { nextPlanYear, parsePlanName, planGardensOf, planNameFor, planYearOf } from './plan'
 
 describe('plan names', () => {
   it('round-trips the default copy name', () => {
@@ -35,3 +35,15 @@ describe('plan names', () => {
     expect(planGardensOf('Home Garden', gardens).map((g) => g.id)).toEqual([3, 2])
   })
 })
+
+describe('nextPlanYear', () => {
+  it('skips years that already have a plan copy, however the dash was typed', () => {
+    const names = ['Back Yard', 'Back Yard — 2027', 'Back Yard - 2028', 'Front Strip — 2029']
+    expect(nextPlanYear('Back Yard', names, 2027)).toBe(2029)
+    expect(nextPlanYear('Front Strip', names, 2027)).toBe(2027)
+  })
+
+  it('is the starting year when nothing is taken', () => {
+    expect(nextPlanYear('Plot', [], 2030)).toBe(2030)
+  })
+})