Fix #2330: Escape angle brackets in man page output

[rodionsteshenko]

Problem

Angle brackets in command Use, Short, Long, and flag Usage strings were stripped by md2man, which interpreted them as HTML tags. This caused placeholders like [<remote>:]<instance> to render as [:] in man pages.

Reported in #2330 by @stgraber (Incus project).

Fix

Added escapeAngleBrackets() which replaces < with \\< and > with \\> before the markdown is passed to md2man. Applied to:

• cmd.UseLine() in SYNOPSIS
• cmd.Short in NAME
• Description (Long/Short) in DESCRIPTION
• flag.Usage in OPTIONS

Test

Added TestGenManAngleBracketsPreserved that creates a command with angle-bracketed placeholders in Use, Short, and Long, generates a man page, and verifies the angle brackets survive in the rendered output.

• Without the fix: test fails — output contains transfer [:] [:] (all placeholder names stripped)
• With the fix: test passes — output preserves <remote>, <source>, <dest>

Tested locally on macOS ARM (Apple Silicon). Full test suite passes.

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