fix(viewer): use bundled Lucide controls across desktop themes

[TheRealShek]

Problem:
Desktop icon themes change the Viewer controls. Yaru turns Close red and supplies thin, detailed toolbar artwork.

Solution:
Bundle 18 Lucide 1.57.0 SVGs with app-specific names, a plain close symbol and explicit 16px sizing. Preserve Lucide's geometry and strokes while adapting paint attributes for GTK. Apply monochrome hover, focus, pressed and disabled states. Retain upstream notices in the binary and installed license files. Viewing remains offline.

Tests:

• Passed formatting, Clippy, 195 unit tests and release build. The separate icon test passed 162 theme/size rendering cases. Other desktop/fixture tests remain ignored.
• Passed seven source-install tests, including notice installation, removal and ownership protection; ShellCheck, shell syntax, desktop-file and AppStream checks. RPM spec validation skipped because rpmspec is unavailable.
• Inspected actual Arch/Wayland before/after captures. Quick Markup enter/cancel passed. Standards and spec reviews found no actionable issues.

Note:
The author tested the final 16px build on Arch/Wayland, approved its appearance, and requested merge and release. Required Fedora CI passed. Full Fedora/GNOME and actual compositor fractional-scale human testing remain unconfirmed. Two-axis final code review found no blocking issues.

Before and after:
Yaru-blue, the same photo and a 966 × 1056 window.

Before	After, Lucide

[coderabbitai]

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