Make every identity editable: agent and operator names plus avatars

- Migration 049: avatar_emoji/avatar_color on agents and employees
- updateAgent accepts a new name (mention-name validated) and avatar;
  new updateEmployeeProfile renames the operator and sets their avatar
- Avatars are emoji-on-color tiles (renderer CSP blocks remote images);
  an AvatarDirectoryContext built from the snapshot lets the shared
  Avatar component honor custom looks at every call site - chat rows,
  conversation list, org chart, office card, sidebar - without
  threading props through pages
- Team edit dialog gains Name + avatar editor (CEO included); the
  sidebar foot opens an Edit-profile dialog for the operator
- e2e: rename an agent to a new mention handle with an emoji avatar,
  edit the operator profile, both verified in the live shell

src/shared/ipc.ts

@@ -7,6 +7,7 @@ export const IPC_CHANNELS = {
   createOrganization: "agentcompany:create-organization",
   createAgent: "agentcompany:create-agent",
   updateAgent: "agentcompany:update-agent",
+  updateEmployeeProfile: "agentcompany:update-employee-profile",
   createTask: "agentcompany:create-task",
   updateTask: "agentcompany:update-task",
   deleteTask: "agentcompany:delete-task",