Address review: shared PlantChip + named recent-plants cap

Gadfly on #100:
- Extracted the tap-to-arm chip (icon + name + armed state) into a shared
  PlantChip, used by both RecentPlants and SeedTray, so the two quick-pick
  surfaces can't drift. SeedTray composes it (rounded={false}) with its
  remove button into one seamless pill.
- Named the recent-strip cap: RECENT_PLANTS_MAX = 8, was a bare slice(0, 8).

Verified live: recent chips and the tray render identically post-refactor.

Co-Authored-By: Claude Opus 4.8 (1M context) <[email protected]>
Claude-Session: https://claude.ai/code/session_01H3zbym8Doka2d7D48maSgZ

web/src/pages/GardenEditorPage.tsx

@@ -45,6 +45,10 @@ import { ApiError } from '@/lib/api'
 
 const routeApi = getRouteApi('/gardens/$gardenId')
 
+// How many recently-planted chips the Plants-mode quick strip shows — a working
+// set, not the whole history; the picker covers the long tail.
+const RECENT_PLANTS_MAX = 8
+
 export function GardenEditorPage() {
   const { gardenId } = routeApi.useParams()
   const gid = Number(gardenId)
@@ -118,7 +122,7 @@ export function GardenEditorPage() {
   const recentPlants = useMemo(
     () =>
       recentlyPlantedIds(plantings)
-        .slice(0, 8)
+        .slice(0, RECENT_PLANTS_MAX)
         .map((id) => plantsById.get(id))
         .filter((p): p is Plant => !!p),
     [plantings, plantsById],