v0.3.7

ship platform-specific postgres binaries only

Once the electron-builder upgrade surfaced the real Windows error, it
was clear: every build was bundling all three platforms' postgres
binaries (macos-arm64, linux-x64, windows-x64). On Windows the macOS
PostGIS extension files are symlinks the Windows filesystem rejects
('WARNING: The directory name is invalid'), which crashed the build.

Move each postgres-bin subdir into the platform-specific
extraResources block. Each build now ships only its own postgres
binaries — the build succeeds, and the resulting artifacts are
smaller (no more carrying ~600MB of unusable cross-platform binaries).

Bumps desktop version to 0.3.7.