style(desktop): restore detailed macOS whale icon

[LouF666]

Summary

• Depends on fix(desktop): restore macOS icon safe area #7123 and intentionally remains a draft until that packaging fix lands.
• Replace only the macOS-specific SVG and ICNS with the detailed whale artwork while retaining the exact 100..924 (824×824) safe area introduced by the dependency PR.
• Keep the shared Windows and Linux full-canvas icon assets unchanged.

The detailed artwork was originally contributed by @SivanCola in #4321. The macOS safe-area adaptation follows the direction proposed by @idoaix in #6156. Both authors are retained as Co-authored-by trailers in this PR's artwork commit.

After #7123 merges, this branch will be rebased onto main-v2 and moved out of draft.

Issues

Refs #6156

Verification

• (cd desktop && go test . -run 'Test(DarwinICNS|AppIconPNG|WindowsICO|DesktopPackagesPreserveNativePlatformLaunchers)')
• (cd desktop && go test ./...)
• (cd desktop && go vet ./...)
• Confirmed the committed ICNS ic10 frame has a 1024×1024 canvas and exact visible bounds of (100,100)-(924,924).
• Applied the same detailed ICNS to Reasonix 1.18.0 on macOS 15.7.8 and visually checked it in Dock and Launchpad against adjacent applications.

Cache impact

Cache-impact: none — this only replaces macOS artwork; provider-visible prompts and request serialization are untouched.
Cache-guard: Existing cache-sensitive surfaces are untouched; the ICNS bounds regression test from dependency PR #7123 covers this asset.
System-prompt-review: N/A