Document on_output option in Bash.run/3

[lostbean]

Motivation

Bash.run/3 passes opts through to Session.execute/3, which supports :on_output for streaming output as it's produced. The streaming works, but Bash.run/3's docstring doesn't mention it. The only documentation for :on_output is on Session.execute/3 directly. Users of the convenience API have no way to know streaming is available without diving into internals, which leads to bypassing Bash.run/3 entirely and calling Bash.parse/1 + Bash.Session.execute/3 directly.

Requirements

1. Add :on_output to Bash.run/3's @doc as a supported option, with the same description as Session.execute/3.
2. Add a usage example showing streaming.
3. If on_output is intentionally unsupported through run/3, document that and raise if passed.

Validations

chunks = []
Bash.run("echo hello", nil, on_output: fn event -> send(self(), event) end)
assert_receive {:stdout, "hello\n"}

Purely a documentation change — the code already works.

• Added test confirming on_output works through Bash.run/3
• Full test suite passes (no regressions)