feat(install): fix setup_shell function for brew users

[better-salmon]

Fixing the install script for brew users

Issue

When installing fnm via Homebrew, the binary gets installed to Homebrew's directory structure rather than the default INSTALL_DIR. Additionally, Homebrew automatically adds fnm to the PATH, making our manual PATH manipulation unnecessary and potentially problematic.

Changes

• Set a USE_HOMEBREW flag to false by default
• Updated shell configuration for all supported shells (zsh, fish, bash) to handle Homebrew installations differently:
  • For Homebrew installations: only add eval "$(fnm env)" to shell config files
  • For direct installations: maintain existing behavior with PATH manipulation
• Simplify shell configuration when Homebrew is used, avoiding redundant PATH modifications

These changes ensure fnm works correctly regardless of installation method, while respecting the environment setup performed by package managers.

Fix #824 #1190 #1194 #1237 #1279 #1376

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Name	Status	Preview	Comments	Updated (UTC)
fnm	✅ Ready (Inspect)	Visit Preview	💬 Add feedback	Apr 28, 2025 6:52am

[polybuildr]

👋 @Schniz looks like this PR and https://github.com/Schniz/fnm/pull/1362 both attempt to fix this issue, do you think one of them could be merged soon? Fresh installs following the instructions at https://nodejs.org/en/download still seem to fail on MacOS due to these bugs.