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>

src/app.h

@@ -486,6 +486,10 @@ public:
      */
     void reloadThemeImages(const std::string& bgPath, const std::string& logoPath);
 
+    // Load / recolor-per-theme the DragonX header logo (SVG rasterized to the theme accent). Called at
+    // the top of render() so the wizard, lock screen, and main header all show it.
+    void ensureLogoTexture();
+
     // Wizard / first-run
     WizardPhase getWizardPhase() const { return wizard_phase_; }
     bool isFirstRun() const;
@@ -1080,6 +1084,7 @@ private:
     int logo_h_ = 0;
     bool logo_loaded_ = false;
     bool logo_is_dark_variant_ = true; // tracks which variant is currently loaded
+    ImU32 logo_accent_ = 0;            // theme accent the SVG logo was last rasterized with (re-render on change)
 
     // Coin logo texture (DragonX currency icon, separate from wallet branding)
     ImTextureID coin_logo_tex_ = 0;