ringgroups: ring-all and hunt groups, API, page, golden case

/api/ring-groups CRUD with members as ordered memberIds (unique, must
exist), number from the ring-group range, a no-answer destination
(never itself), and delete refused while something points at it. The
generator renders sp-rg-{id} (Dial through sp-rg-member: all at once with
the total ring time, or one at a time with the per-member time, music
instead of ringing on request), adds the number to sp-local-numbers, and
destApp sends ring_group destinations there. Golden case ringgroups.

The DestinationPicker is now generic over targets picked by id and gains
"Voicemail of a user" and "Ring group" (M6-T6 completes it). Caller-name
prefixes (DIDs and ring groups) get a space before the caller's name.
Ring groups page with an ordered member list.

e2e m6-t2 found the new-group form failing on an unset no-answer
destination (fixed: defaults to hang up). It checks ring-all (both ring,
191 answers) and hunt (190 alone for 5 s, then 191) with real calls. The
generator debounce test now waits for the apply instead of a fixed 150 ms.

Task: M6-T2

docs/spec/03-config-generator.md

@@ -569,6 +569,9 @@ exten => s,1,Set(__SP_TARGET=500)
 ```
 With zero members, leave out the Dial lines.
 Ring groups deliberately **ignore** members' call forwarding and send nobody to voicemail.
+The caller-name prefix (here and on DIDs) goes through `name()`, which trims, so one space is
+always put between it and the caller's name: `Set(CALLERID(name)={prefix} ${CALLERID(name)})`.
+Golden case `ringgroups`; `scripts/e2e/m6-t2.mjs` checks ring-all and hunt with real calls (M6-T2).
 
 ### 6.8 Queues