feat: add endpoint and CLI for users to view their own OIDC claims (#23053)

- Adds a new API endpoint `GET /api/v2/users/oidc-claims` that returns
only the **merged claims** (not the separate id_token/userinfo
breakdown). Scoped exclusively to the authenticated user's own identity
— no user parameter, so users cannot view each other's claims.
- Adds a new CLI command:** `coder users oidc-claims` that hits the
above endpoint.
- The existing owner-only debug endpoint is preserved unchanged for
admins who need the full claim breakdown.


> 🤖 This PR was created with the help of Coder Agents, and will be
reviewed by my human. 🧑‍💻

cli/users.go

@@ -19,6 +19,7 @@ func (r *RootCmd) users() *serpent.Command {
 			r.userSingle(),
 			r.userDelete(),
 			r.userEditRoles(),
+			r.userOIDCClaims(),
 			r.createUserStatusCommand(codersdk.UserStatusActive),
 			r.createUserStatusCommand(codersdk.UserStatusSuspended),
 		},