feat: oversize sheets, image duplication, free labelling and a new layout

Prints larger than the sheet no longer just fail. Each cell can now spill over
the whole sheet (20x30 on A4 loses exactly 3 mm, and says so beforehand) or be
tiled across several sheets with a dashed glue fold and a sheet number. The
maths lives in printoversize.ts, dependency-free, so the browser preview and the
server PDF compute the same thing -- including the note strip that keeps the
sheet number off the picture.

The same image can now appear as several cells, so a portrait can be printed at
two sizes on one sheet without copying and re-uploading the file. The footer
line can be switched off, given custom text and placed at one of six positions;
it is only drawn where that edge is free.

Layout reworked for all three widths: work left, sticky preview right on the
desktop, collapsed setting groups paired in a two-column grid that expands full
width; preview first and a fixed action bar on the phone. Verified at 390, 820,
1440 and 1680 px -- no horizontal overflow, no dead white space.

Also a public presentation page at /vorstellung (no login, nothing operable),
whose sample sheet is computed by the real packer rather than drawn.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01BNhLunz586g6DeYMa7Qsd1

CHANGELOG.md

@@ -2,6 +2,47 @@
 
 All notable changes to Klarbild are documented here. Newest first.
 
+## 2026-08-20 — Oversize sheets, duplicate images, free labelling, new layout
+
+### Added
+- **Prints larger than the sheet.** The everyday case is 20 × 30 cm on A4 photo paper, where
+  exactly 3 mm are missing. Instead of refusing, each cell now offers two ways out
+  (`src/lib/printoversize.ts`, dependency-free like `printlayout.ts` so browser and server compute
+  the same thing):
+  - `overflow` centres the piece on the **whole sheet**, not the printable area — otherwise you
+    throw away the margin a borderless printer can actually use. How much is lost per side is
+    computed up front and shown before printing.
+  - `tile` splits the piece across several sheets. Tiles overlap by a glue fold (10 mm by default),
+    printed on both neighbours and marked with a dashed line. Each sheet carries its number, row
+    and column. 30 × 40 cm on A4 → 2 × 2 sheets.
+  Verified by rasterising the PDFs at 254 dpi: the overflow case measures 200,1 mm wide at x = 5 mm
+  and bleeds off both long edges; the tiles measure 200 × 286 and 110 × 124 mm, overlapping by 10.
+- **Duplicate an image.** The same picture can now appear as several cells and be printed in two
+  different sizes on one sheet. Previously you had to copy the file, rename it and upload it again.
+- **Configurable label.** The footer line can be switched off, given custom text, and placed at one
+  of six positions. It is only drawn if that edge is actually free — it never lands on a picture.
+- **Public presentation page** at `/vorstellung` (no login, nothing operable). The sample sheet on it
+  is not a drawing: it runs the real packer at render time, so it follows the algorithm.
+
+### Fixed
+- **The tile number overlapped the picture.** The sheet number is printed at 8 pt from 3 mm off the
+  top edge, which needs about 6 mm — with a 5 mm paper margin it ran 0,8 mm into the motif.
+  `noteInset()`/`tileSheet()` now shift the tile down by the shortfall and shorten the sheet by the
+  same amount, so nothing sticks out at the bottom. Both the browser preview and the PDF call the
+  same helper, so the previewed sheet count cannot drift from the printed one.
+
+### Changed
+- **Desktop layout.** Work on the left, preview on the right, and the preview column is sticky so it
+  follows along — no more endless column next to an empty one. Setting groups sit collapsed side by
+  side in a two-column grid and expand across the full width, so three-way switches keep their
+  labels instead of being squeezed to 50 px.
+- **Mobile layout.** Preview first, "Druck-PDF erzeugen" as a fixed bar above the tab navigation,
+  each image row showing thumbnail and controls side by side, touch targets at 38–40 px, and the
+  remove button moved onto the thumbnail so it stops covering the format dropdown. The step numbers
+  ("1 ·", "2 ·") are hidden below 1080 px, where the preview comes first and the numbers would lie.
+- Advanced setting groups (margins, quality, labelling, delivery) start collapsed — their summary
+  line already says what is set.
+
 ## 2026-08-18 (4) — Renamed to "Drucken", 86 sizes, crop editor fixed
 
 ### Fixed