Use plain binary name inside release archives

[alexrinass]

Release archives currently contain binaries with version and platform baked into the filename (e.g. git-flow-v1.0.0-windows-amd64.exe). This forces users to rename the binary after extraction on every platform before it can be used as a Git subcommand.

The standard convention for CLI tools is to use the plain binary name inside the archive, with version/platform info only in the archive filename.

Current behavior

git-flow-next-v1.0.0-windows-amd64.zip
  └── git-flow-v1.0.0-windows-amd64.exe   # user must rename to git-flow.exe

git-flow-next-v1.0.0-darwin-arm64.tar.gz
  └── git-flow-v1.0.0-darwin-arm64         # user must rename to git-flow

Expected behavior

git-flow-next-v1.0.0-windows-amd64.zip
  └── git-flow.exe                         # works immediately

git-flow-next-v1.0.0-darwin-arm64.tar.gz
  └── git-flow                             # works immediately

Prior art

Every major Go CLI tool follows this convention:

Tool	Archive name	Binary inside
gh (GitHub CLI)	gh_2.89.0_macOS_arm64.zip	gh
ripgrep	ripgrep-15.1.0-aarch64-apple-darwin.tar.gz	rg
fzf	fzf-0.71.0-darwin_arm64.tar.gz	fzf
lazygit	lazygit_0.60.0_darwin_arm64.tar.gz	lazygit

This is also the GoReleaser default behavior.

Scope

• Update scripts/build.sh to build binaries with the plain name (git-flow / git-flow.exe)
• Archive filenames keep version/platform info (no change)
• Simplify manual installation docs (rename step becomes unnecessary)