License under AGPL-3.0-only

Ensures anyone running a modified version of C3 as a network service
has to share their changes back, not just users who redistribute the
binary.

- LICENSE: full AGPLv3 text with copyright notice filled in
- Cargo.toml: license = "AGPL-3.0-only"
- README: brief license section

Cargo.toml

@@ -2,6 +2,7 @@
 name = "CCC"
 version = "0.1.0"
 edition = "2024"
+license = "AGPL-3.0-only"
 
 [dependencies]
 urus = { git = "https://git.kalsbeek.dev/Markk116/urus.git" }