[Track C] Add a tiny applications subsection to notes/StoneWeierstrassC0.tex

[przchojecki]

Path: notes/StoneWeierstrassC0.tex

This is a small, note-only starter issue.

Task:

• add a short applications subsection listing one or two concrete approximation corollaries that should eventually follow from the real C0 Stone-Weierstrass theorem
• keep it to short theorem or corollary statements only

Acceptance criteria:

• the new subsection lands in notes/StoneWeierstrassC0.tex
• it lists one or two concrete downstream corollaries
• the PR does not turn into a full applications chapter