[Good First Issue] Add HTML export option for optimized content

[mverab]

Currently, optimized content is exported as markdown. Add option to export as HTML.

What's needed:

1. Add --format flag to /geo:optimize command
2. Support markdown (default) and html formats
3. Convert markdown to HTML while preserving formatting

Example:

/geo:optimize content.md --format html
# Creates: geo-output/optimized/content.html

Resources:

• Python markdown library: https://pypi.org/project/markdown/
• Current export logic in commands