rename logo assets: logo-* and appicon-* sets

Two clean sets from their SVG sources:
  logo.svg    → logo-{16..1024}.png (bare, transparent)
  appicon.svg → appicon-{16..1024}.png (on dark circle)
All rendered from 2048px masters. References updated in
pubspec.yaml, welcome view, and native runner.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

pubspec.yaml

@@ -64,14 +64,10 @@ flutter:
     - assets/fonts/jetbrains_mono/OFL.txt
     - assets/fonts/josefin_sans/OFL.txt
     - assets/fonts/phosphor/LICENSE
-    - assets/logo/clide-logo.svg
-    - assets/logo/clide-logo-16.png
-    - assets/logo/clide-logo-32.png
-    - assets/logo/clide-logo-48.png
-    - assets/logo/clide-logo-192.png
-    - assets/logo/clide-logo-256.png
-    - assets/logo/clide-logo-512.png
-    - assets/logo/clide-logo-1024.png
+    - assets/logo/logo.svg
+    - assets/logo/logo-192.png
+    - assets/logo/appicon.svg
+    - assets/logo/appicon-256.png
     - assets/grammars/
     - assets/queries/