Generated MD file documentation should follow MD041/first-line-heading/first-line-h1: First line in a file should be a top-level heading

[PaulMEdwards]

I use the markdownlint VSCode extension and it complains about MD041/first-line-heading/first-line-h1: First line in a file should be a top-level heading on all the OpenSpec generated documentation MD files.

It would be ideal to have these headings as the first line, followed by a blank line, in the respective generated files:

File	Heading
proposal.md	# Proposal
design.md	# Design
spec.md	# Specifications or # Requirements
tasks.md	# Tasks