fix(macos): pad dock icon to Apple icon grid (#1169)

* fix(macos): pad dock icon to Apple icon grid

The macOS .icns artwork filled the canvas edge-to-edge, so the dock icon
rendered larger than native apps. Replace icon.icns with a build whose artwork
is scaled to an ~824px body centred on a 1024px transparent canvas (Apple's
icon grid). macOS-only asset; Windows .ico and Linux PNGs unchanged. Refs #1166.

* fix(macos): skip the icns app-icon in dev to avoid a launch crash

Tauri's dev-only macOS path sets the app icon from icon.icns via
NSImage::initWithData(...).expect(...) (RunEvent::Ready); the padded icns
makes that return nil and abort at launch — release builds are unaffected.
Add a dev config override (tauri.dev.conf.json) that drops icon.icns from
bundle.icon so the dev app icon falls back to a PNG; tauri:dev passes it via
--config. Production bundling keeps the padded icon.icns. Refs #1166.

* docs(changelog): add entry for macOS dock icon padding (PR #1169)

src-tauri/tauri.dev.conf.json

@@ -0,0 +1,10 @@
+{
+  "bundle": {
+    "icon": [
+      "icons/32x32.png",
+      "icons/128x128.png",
+      "icons/128x128@2x.png",
+      "icons/icon.ico"
+    ]
+  }
+}