Add man (manual pages) support to agentos-shell

[NathanFlurry]

man is not available in just shell today.

Needed

• Provide the man command plus a man-page source/format path (mandoc or groff-rendered pages) as WASM registry software in secure-exec registry/software/.
• Add it to the agentos-shell software list (packages/shell/src/main.ts).

Notes

• Consider shipping pre-rendered (cat) man pages to avoid bundling groff, and wiring MANPATH to a guest directory.
• Lower effort than a full pager/editor; mostly packaging + page content.

Part of making just shell a complete interactive environment.