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.lock

@@ -7866,3 +7866,15 @@ dependencies = [
  "syn 2.0.114",
  "winnow 0.7.14",
 ]
+
+[[patch.unused]]
+name = "cosmic-config"
+version = "1.0.0"
+
+[[patch.unused]]
+name = "cosmic-theme"
+version = "1.0.0"
+
+[[patch.unused]]
+name = "libcosmic-yoda"
+version = "0.1.0-yoda.2"