feat(planner): align tile design with spec

Front face:
- Full dual gradient overlay (dark top 32% → transparent → dark bottom 55%)
- Day abbreviation + date number pill at top of each tile
- Recipe name 13px/weight-300 with text-shadow
- Meta line (cookTimeMin · effort) below name
- Glassmorphism tag pills (protein + cuisine only)
- State rings via box-shadow (yellow for today, green for selected)
- Dimming (opacity 0.42) on non-selected filled tiles

Back face:
- Koch-Modus as green primary button
- Entfernen as red outline (transparent bg)
- All buttons 11px / weight 500

EmptyDayTile: add day header + spec-aligned suggestion list layout
Page: remove external column header (now rendered inside each tile)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/routes/(app)/planner/+page.svelte

@@ -477,26 +477,9 @@
 					{#each days as day (day)}
 						{@const slot = slotMap[day] ?? { id: null, slotDate: day, recipe: null }}
 						{@const isTodayDay = day === today}
-						{@const dateNum = day.slice(-2).replace(/^0/, '')}
-						{@const dayAbbr = formatDayAbbr(day, 'narrow')}
 						{@const isThisTileActive = drawerSlotId === day}
 
-						<div class="flex h-full flex-col">
-							<!-- Column header -->
-							<div class="mb-2 flex flex-col items-center gap-1">
-								<p class="font-[var(--font-sans)] text-[9px] uppercase tracking-wide text-[var(--color-text-muted)]">
-									{dayAbbr}
-								</p>
-								<div
-									class="flex h-6 w-6 items-center justify-center rounded-full text-[11px] font-medium
-										{isTodayDay ? 'bg-[var(--yellow)] text-white' : 'bg-transparent text-[var(--color-text)]'}"
-								>
-									{dateNum}
-								</div>
-							</div>
-
-							<!-- Flip tile -->
-							<div class="min-h-0 flex-1">
+						<div class="h-full">
 								<DesktopDayTile
 									{slot}
 									isToday={isTodayDay}
@@ -511,7 +494,6 @@
 									onremove={() => handleTileRemove(slot)}
 									onaddrecipe={() => handleEmptyTileAdd(day)}
 								/>
-							</div>
 						</div>
 					{/each}
 				</div>