feat(ui): themed DragonX logo — runtime-rasterized SVG recolored per skin

Replace the shared app logo (Overview header, first-run wizard, lock screen) with
the DragonX mark rendered from res/img/logos/logo_dragonx.svg, recolored to each
theme: the dragon body takes the theme accent (Primary()), the inner detail stays
light. Vendor nanosvg (memononen, zlib/public-domain) in libs/nanosvg/ and add
util::LoadTextureFromSvg (parse a copy, recolor shapes by luminance, rasterize to
RGBA, upload via the existing CreateRawTexture — GL + DX11). The SVG is embedded as
a string (src/embedded/logo_dragonx_svg.h) so it's available in every build.

The load moves into App::ensureLogoTexture(), called at the top of render() BEFORE
the wizard/lock early-returns (so those screens get the logo too, which they never
did before), and re-rasterizes when the accent or the dark/light variant changes.
The per-skin PNG remains a fallback if rasterization ever fails; logo-texture
lifetime is now freed on replace + on theme switch (was leaked).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

res/img/logos/logo_dragonx.svg

@@ -0,0 +1,23 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<svg id="Layer_1" data-name="Layer 1" xmlns="http://www.w3.org/2000/svg" viewBox="0 0 128 128">
+  <defs>
+    <style>
+      .cls-1 {
+        fill: #fff;
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+
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