numbers: any free internal number of 1 to 6 digits; ranges only suggest

Owner wanted the first user on 1. Numbering ranges now choose the Next free suggestion
(Settings → Numbering), the setup wizard takes a number per person, and a one-digit number
can't also be a menu key of a digital receptionist with direct dialing. Dialplan patterns that
take an internal number match one digit (_X!); golden case short-numbers proves it in Asterisk.

apps/api/test/ringgroups.test.ts

@@ -64,7 +64,7 @@ describe.skipIf(!hasTestDb)('/api/ring-groups', () => {
         noAnswerDestination: { type: 'hangup' },
         ...body,
       });
-    expect((await bad({ number: '101' })).statusCode).toBe(400); // outside 500–549
+    expect((await bad({ number: '101' })).statusCode).toBe(409); // extension 101 has it
     expect((await bad({ number: '500' })).statusCode).toBe(409);
     expect((await bad({ memberIds: [ext['101'], ext['101']] })).statusCode).toBe(400);
     expect((await bad({ memberIds: ['00000000-0000-4000-8000-000000000999'] })).statusCode).toBe(