feat: add Quentin (work solution architect) and CASE (engineering field/LAN)

- Add Quentin as work-team lead agent for solution architecture & demos,
  with aws_sa repositioned as Quentin's exclusive subagent (tool, not peer)
- Add CASE as engineering lead agent for field/physical layer (LAN, hardware)
- Bump unified Neo4j schema to v2.4.0:
  - Add Solution and Demo node types under Quentin's domain
  - Update assistant ownership table with Quentin, CASE, and AWS SA scoping
- Update README and neo4j shared docs to reflect new team rosters and
  subagent boundaries

docs/tools/neo4j/shared.md

@@ -137,12 +137,13 @@ to keep in sync.
 | Team | Assistants |
 |------|-----------|
 | **Personal** | shawn, nate, hypatia, marcus, watson, bourdain, david, cousteau, garth, cristiano |
-| **Work** | alan, ann, jeffrey, jarvis, aws_sa |
-| **Engineering** | scotty, harper |
+| **Work** | alan, ann, jeffrey, jarvis, quentin |
+| **Engineering** | scotty, harper, case |
 
 Watson replaces Seneca (as of 2026-04-28); David replaces Bowie; Shawn is the
-personal general assistant (calendar/contacts/email). AWS SA is the work-team
-cloud-architecture specialist.
+personal general assistant (calendar/contacts/email). Quentin is the work-team
+solution architect; aws_sa is Quentin's subagent (called as a tool, not a
+messaging peer) — see [work/subagents.md](../../work/subagents.md).
 
 ## Graph Error Handling