dids: phone numbers, destinations, inbound dialplan, Phone numbers page

DIDs CRUD (any input format, normalized; 409 on duplicates; a number
that is an emergency or default caller ID can't be removed). Shared
destination service: assertDestinationExists, describeDestination
("Ring Dan Doe (101)") and findReferences over every destination
column in 02 §1 plus the unmatched-number setting; deleting an
extension a destination points at is now a 409 naming the places.

Generator: destApp (user, external, hangup for now), sp-from-trunk-*
per enabled trunk, sp-did-exists (left out when empty) and sp-inbound
with caller-name prefix. Golden case voipms-basic. Phone numbers page
with a minimal DestinationPicker (user, outside number, hang up).

trunk-test.ts: the fake provider calls the DID with a 10-digit
Request-URI like voip.ms; baresip 101 answers, caller ID arrives
normalized, 500 packets each way on both legs. scripts/e2e/m3-t2.mjs
checks the UI → Asterisk path. Still to do with real voip.ms: the
mobile-to-DID call and recording which header carries the DID (06 §3).

Task: M3-T2

docs/spec/03-config-generator.md

@@ -514,6 +514,8 @@ exten => 13125551234,1,Set(__SP_DID=13125551234)
 ; anything else
 exten => _[0-9a-z].,1,{destApp(routing.unmatchedDidDestination)}
 ```
+Leave `[sp-did-exists]` out when there are no DIDs: Asterisk doesn't create an empty context, and
+`DIALPLAN_EXISTS` on a missing context is simply false. `record_inbound` arrives with recording (M7).
 
 ### 6.6 `sp-local-numbers`