feat: v0.2.0 — Groups (@group routing, roles, wizard)

Phase A of the claudemesh spec. Peers can now join named groups
with roles, and messages route to @group targets.

Broker:
- @group routing in fan-out (matches peer group membership)
- @all alias for broadcast
- join_group/leave_group WS messages + DB persistence
- list_peers returns group metadata
- drainForMember matches @group targetSpecs in SQL

CLI:
- join_group/leave_group MCP tools
- send_message supports @group targets
- list_peers shows group membership
- PeerInfo includes groups array
- Peer name cache for push notifications

Launch:
- --role flag (optional peer role)
- --groups flag (comma-separated, e.g. "frontend:lead,reviewers")
- Interactive wizard for role + groups when flags omitted
- Groups written to session config for broker hello

Spec: SPEC.md added with full v0.2 vision (groups, state, memory)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

packages/db/migrations/0007_add-presence-groups.sql

@@ -0,0 +1 @@
+ALTER TABLE "mesh"."presence" ADD COLUMN "groups" jsonb DEFAULT '[]'::jsonb;