Resolve Hermit binary from PATH in shell hooks

[Noot-tooN]

Summary

• resolve the installed hermit executable from PATH when generating Bash, Zsh, and Fish shell hooks
• quote the resolved executable path so installations in paths containing spaces work
• execute the generated snippets in real Bash, Zsh, and Fish processes during tests
• install Fish and Zsh in the CI test job so every supported shell is exercised

Why

The generated shell-hook configuration assumed Hermit was installed at $HOME/bin/hermit. Installations managed elsewhere, such as Homebrew at /opt/homebrew/bin/hermit, therefore produced an inactive hook: entering a Hermit environment did not update PATH, so project tools such as npx remained unavailable.

The hook installer now locates the same hermit executable already available on PATH while preserving an explicitly configured HERMIT_ROOT_BIN.

Validation

• go test -count=1 ./...
• ./bin/golangci-lint run
• ./bin/lint-shell-scripts
• git diff --check

[Noot-tooN]

Not sure how the maintainers of this repo would feel about this, but i don't see any proper way to test this feature out without this. 😄