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/conferences.test.ts

@@ -62,7 +62,7 @@ describe.skipIf(!hasTestDb)('/api/conferences', () => {
   it('checks the number and the PINs', async () => {
     const bad = (body: object) =>
       req('POST', '/api/conferences', { number: '801', name: 'X', ...body });
-    expect((await bad({ number: '700' })).statusCode).toBe(400); // parking, not 800–849
+    expect((await bad({ number: '700' })).statusCode).toBe(409); // the parking lot
     expect((await bad({ number: '800' })).statusCode).toBe(409);
     expect((await bad({ pin: '12' })).statusCode).toBe(400);
     expect((await bad({ pin: '12a4' })).statusCode).toBe(400);