Group chat with E2E encryption for both web and CLI clients

Server:
- POST /v1/groups/create — create named group
- POST /v1/groups/:name/join — join group
- GET /v1/groups/:name — get group info + member list
- GET /v1/groups — list all groups
- POST /v1/groups/:name/send — fan-out encrypted messages to members
- Groups stored in sled, members tracked by fingerprint

Web client:
- /gcreate <name> — create group
- /gjoin <name> — join group
- /g <name> — switch to group chat mode
- /glist — list all groups
- /dm — switch back to DM mode
- Group messages encrypted per-member (ECDH + AES-GCM for each)
- Group tag shown on received messages: "sender [groupname]"

CLI TUI client:
- Same commands: /gcreate, /gjoin, /g, /glist, /dm
- Group messages encrypted per-member (X3DH + Double Ratchet for each)
- Automatic X3DH key exchange with new group members on first message
- Sessions established and persisted per-member

Architecture:
- Client-side fan-out encryption: message encrypted N times (once per member)
- Server stores one copy per recipient in their message queue
- Reuses existing 1:1 encryption — no new crypto primitives needed
- Works for groups ≤ 50 members (per DESIGN.md)

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

warzone/crates/warzone-server/src/routes/mod.rs

@@ -1,3 +1,4 @@
+mod groups;
 mod health;
 mod keys;
 mod messages;
@@ -12,6 +13,7 @@ pub fn router() -> Router<AppState> {
         .merge(health::routes())
         .merge(keys::routes())
         .merge(messages::routes())
+        .merge(groups::routes())
 }
 
 /// Web UI router (served at root, outside /v1)