One namespace for internal numbers (range, reserved codes, parking, every
object table) with a next-free lookup. Creating an extension generates its
SIP password and voicemail PIN and a runtime-state row; every change and
password regeneration triggers a config apply. Credentials are revealed
only on request and each reveal is audited. Users get an Ext. column and a
drawer with General (number + next free), Phone and Credentials tabs.
scripts/e2e/m2-t5.mjs checks the flow in a browser and that the generated
PJSIP file follows; the files it produced load cleanly in Asterisk.
Task: M2-T5
