fix(magic_data): detect bash/sh/zsh shell script shebangs as .sh (#150)

[SAY-5]

Summary

Fixes #150. magic_data.json had Python and PowerShell shebang patterns but no entries for the much more common Unix shell shebangs, so a file starting with #!/bin/bash was matched only by the generic ascii text fallback and reported as .txt / text/plain. The reporter hit this on a real .sh file with v2.1.1.

Change

puremagic/magic_data.json, add hex-encoded shebang patterns for the standard shells:

• POSIX sh: #!/bin/sh, #! /bin/sh, #!/usr/bin/sh, #!/usr/bin/env sh\n → .sh / application/x-sh
• Bourne-again (bash): #!/bin/bash, #! /bin/bash, #!/usr/bin/bash, #!/usr/bin/env bash, #!/usr/local/bin/bash → .sh / application/x-shellscript
• Z shell (zsh): #!/bin/zsh, #!/usr/bin/zsh, #!/usr/bin/env zsh\n → .sh / application/x-shellscript
• dash: #!/bin/dash → .sh / application/x-sh

The newline-terminated entries (env sh\n, env zsh\n) avoid an over-match where env shell etc. could collide.

Test plan

• pytest test/, 96 passed (was 95; +1 new test)
• New test_bash_shebang_detected covers #!/bin/bash, #!/bin/sh, #!/usr/bin/env bash, #!/bin/zsh, all return .sh
• Existing test_small_stream_error for the python shebang still passes, python entries are unchanged