Export a board to PDF, one page per area or the whole board on one page - #93

…ge (#97)

## Why

Phase E2 of [docs/export.md](docs/export.md), on top of the PowerPoint
export merged in #92. A deck suits a presenter; a PDF suits an attendee
who wants to read, print, or zoom, and PDF has the one freedom a slide
lacks: a page of any size. Replaces #93, which GitHub closed when its
base branch was deleted after the merge.

## What it does

- **PDF is a choice in the same Export dialog.** The dialog relabels
itself (pages rather than slides), hides the slide size and the notes
switch, and shows the page size (A4 or Letter, landscape) and a footer
switch. The areas and the preview are exactly those of the deck, so a
deck and a PDF of the same board agree.
- **One page per area**: the area's picture under a header line with its
title, a bookmark per page, and a footer with the board name, the date,
and "n of m". The overview page comes first when there are at least two
areas.
- **Whole board on one page**: a single page the shape of the board,
rendered at up to 6000 pixels on the longer edge and sized at 144 dpi (a
41-inch page for a 6000-pixel board, under the 200-inch limit viewers
enforce). No header or footer: the page is the board.

## Where the code is

- `SQLBI.Whiteboard.Export/PdfDocumentWriter.cs` over `PdfSharp` 6.2.4
(MIT, managed-only, per decision 21). Fonts are read from the Windows
fonts folder through a small resolver, since PDFsharp's Core build
brings none.
- `ExportSettings` gains the format, page size, and footer;
`BoardExporter` branches on the format and renders the poster larger;
the dialog gains the PDF controls.
- Smoke tests read the produced PDF back: page count, A4 landscape size,
one bookmark per page, and the fit-to-picture page size.

The smaller calls are listed under E2 in
[docs/export-decisions.md](docs/export-decisions.md); decision 26 is
updated, and the 1.3.0 release notes gain their PDF entry.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-authored-by: Claude Fable 5.1 <[email protected]>

#94)

## Why

Phase E3 of [docs/export.md](docs/export.md), on top of #93 (base is the
E2 branch; retarget to `main` once it merges). A picture slide is exact
but dead: a person who wants to rework a deck after a session needs the
DAX to be text and the pictures to be pictures.

## What it does

- **Slide content: Picture or Editable**, a choice on the Export dialog
for PowerPoint. Picture stays the default because it is exact; Editable
is best effort by design.
- **Editable** puts each image on the slide as a picture (PNG and JPEG
bytes as they are, sniffed rather than trusted to the stored content
type; SVG, BMP, and GIF rasterized at the size they take on the slide
through the code the clipboard uses), each text container as a rounded
text box with the language service's title as its first line and the
body as runs carrying the syntax colors and weights the screen shows, a
LiveView as its current frame, and all the ink as one transparent PNG
over everything.
- **Placement is identical to the picture mode**: the rasterizer exposes
the camera it would have used, and every element is mapped through it
into the same picture box.

## Where the code is

- `SQLBI.Whiteboard.Export/ExportPage.cs`: the element model
(`SlideImageElement`, `SlideTextElement`), in page pixel space.
- `PptxDeckWriter`: a slide with elements gets one shape per element in
z-order; the single-picture path is unchanged.
- `SQLBI.Whiteboard/Export/EditableSlide.cs`: builds the elements from
an area; `BoardSurface` gains `DrawBackground` and `ObjectFilter` for
the ink overlay.
- Smoke tests write an editable slide and check its pictures, text box,
runs, and image parts.

The smaller calls are under E3 in
[docs/export-decisions.md](docs/export-decisions.md); decision 26 is
updated.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-authored-by: Claude Fable 5.1 <[email protected]>