Draw an SVG's clipped picture where the author put it - #99

…labels readable (#102)

## Why

Importing an infographic SVG showed two rendering defects. Logos the
file embeds as bitmaps came out at the wrong size: a GitHub Copilot mark
saved at 216 DPI drew at less than half the width of its box, and the
OpenAI and Power BI marks saved at 72 DPI a third too large. And the
lane labels above the arrows, `TOOL CALLS`, `MODEL OPS`, `THE
INTERFACE`, collapsed into an unreadable pile of letters. Chrome draws
the same file as the author meant.

## Cause

Both are SharpVectors 1.8.5 behaviours, checked against its source.

**Bitmap size.** `WpfImageRendering` fits an embedded bitmap into its
`<image>` using the decoded picture's WPF `Width` and `Height`. Those
are device-independent units, so they scale with the DPI the PNG or JPEG
declares: a 1024-pixel PNG at 72 DPI measures 1365 units, a 2200-pixel
PNG at 216 DPI measures 978. Browsers measure pixels. The ratios seen on
the board are exactly 96/72 and 96/216, and stripping the DPI metadata
from a copy of the file made the renderer agree with Chrome.

**Collapsed labels.** `WpfHorzTextRenderer` draws text that has
`letter-spacing` one glyph at a time and gives every glyph the text's
own `TextAlignment`. With `text-anchor="middle"` each glyph is centred
on the pen and the pen advances only half a glyph; with `end` it does
not advance at all. Text anchored at its start goes through the same
path correctly.

## Fix

- `SvgImageCodec` installs a `WpfEmbeddedImageVisitor` that decodes
base64 data URIs itself and returns the same pixels at 96 DPI, so one
unit is one pixel. Everything else, and anything that fails to decode,
falls through to the renderer's own reader, still under
`ExternalResourcesAccessModes.Ignore`.
- `SvgMarkup.Rewrite` (which now also carries the clip hoist from #99,
in a single parse) removes `letter-spacing` from `<text>` and `<tspan>`
whose effective `text-anchor`, own, inherited, or written in `style`, is
`middle` or `end`. The label is then measured and placed as one string,
where the author put it and set slightly tighter than they asked.
Spacing the renderer already ignores, such as a value with a unit, and
spacing on start-anchored text is left alone.

The stored asset is untouched; only what is handed to the renderer
changes. Decision 21 and the 1.3.0 release notes record both.

## Verification

Release build clean, smoke tests pass with new cases for the
letter-spacing rule and the renamed entry point. The rebuilt application
opened a `.wimport` with the reported file: logos match Chrome's sizes
and the lane labels read correctly and centred over their arrows. All
nine SVGs in the same figure set render through the new codec with no
regression, including the clipped-screenshot case from #99.

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

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