Warn when notation type conflicts with document content or available glyphs

### Problem

Neon currently allows users to select Square or Hufnagel notation during upload and to switch the notation type on the edit page.

Neon does not currently check:

- Whether the selected notation type matches the document content.
- Whether the neumes in the document can be displayed correctly using the selected notation type and font.
- Whether switching the notation type would make existing groupings or glyphs incompatible.

### Decisions needed

- Whether validation should occur during upload, when switching on the edit page, or both.
- Whether an incompatibility should block the action or display a warning while allowing the user to continue.
- How to define the supported glyph or neume set for Square and Hufnagel notation.
- How Neon should inform users when a Hufnagel glyph is unavailable but can fall back to Bravura.

### Related issues

- #1372
- Hufnagel font glyph coverage