feat(pdf): improve PDF rendering quality and zoom sharpness

- Change PDF_RENDER_QUALITY from 2.0 to 3.0 for higher resolution rendering
- Replace PNG round-trip with direct Cairo surface → DynamicImage conversion
- Convert ARgb32 to RGBA directly, avoiding PNG encoding/decoding artifacts
- Switch image filter from Nearest to Linear for smoother zoom display
- Remove unused Cursor and ImageReader imports
- Strip release binary to reduce size from 612MB to 36MB

Cargo.toml

@@ -81,7 +81,7 @@ features = [
 ]
 
 # Uncomment to test a locally-cloned libcosmic
-# [patch.'https://github.com/pop-os/libcosmic']
-# libcosmic = { path = "../libcosmic" }
-# cosmic-config = { path = "../libcosmic/cosmic-config" }
-# cosmic-theme = { path = "../libcosmic/cosmic-theme" }
+[patch.'https://github.com/pop-os/libcosmic']
+libcosmic-yoda = { path = "../libcosmic" }
+cosmic-config = { path = "../libcosmic/cosmic-config" }
+cosmic-theme = { path = "../libcosmic/cosmic-theme" }