Set the project license in config.env; AGPL-3.0 default only for a public GitHub project

- PROJECT_LICENSE (a Gitea license key, or none) is read, checked and never asked
- Without it AGPL-3.0 applies only when GitHub is chosen and the project is public
- The license is applied on Gitea with or without GitHub, and checked against the server first
- Plan and summary name the license and where it came from
- MIL-006 accepted; README and config.env.example document the key
- Tests: new test-license.sh; existing tests use a public project where they expect AGPL-3.0

Task: MIL-006#1
Task: MIL-006#2
Task: MIL-006#3
Task: MIL-006#4
Refs #44
Refs #45
Refs #46
Refs #50

src/lib/apply.sh

@@ -47,9 +47,9 @@ confirm_reuse() {
       die "stopped: choose another name or remove the existing repository"
     fi
   done
-  if ((${STATE[reuse_gitea]:-0})) && ((PROJECT[has_github])) &&
+  if ((${STATE[reuse_gitea]:-0})) && [[ -n ${PROJECT[license]} ]] &&
     [[ ${STATE[gitea_repo]} == empty ]]; then
-    warn "the empty Gitea repository is reused as it is: the $AGPL_LICENSE_KEY license is not added to it"
+    warn "the empty Gitea repository is reused as it is: the ${PROJECT[license]} license is not added to it"
   fi
 }