fix: render server nick per user in messages tab and analysis

Extract server_nick from metadata.member.displayName in backend messageMapper,
add server_nick to frontend MessageRecord type, and update messages view +
analysis view to display the member's server-specific nickname (with @username
as secondary context) instead of the global username.

services/frontend/src/app/(dashboard)/analysis/view.tsx

@@ -193,12 +193,21 @@ export function AnalysisView() {
                   key={m.id}
                   className="search-result-card hud-card flex items-start gap-3 p-3 transition-all"
                 >
-                  <Avatar src={m.avatar_url} name={m.username} size={32} />
+                  <Avatar
+                    src={m.avatar_url}
+                    name={m.server_nick ?? m.username}
+                    size={32}
+                  />
                   <div className="min-w-0 flex-1">
                     <div className="flex items-center gap-2">
                       <span className="text-xs font-semibold text-ink">
-                        {m.username}
+                        {m.server_nick ?? m.username}
                       </span>
+                      {m.server_nick && m.server_nick !== m.username && (
+                        <span className="font-mono text-[10px] text-ink-muted">
+                          @{m.username}
+                        </span>
+                      )}
                       <span className="font-mono text-[10px] text-ink-faint">
                         {getMessageChannelLabel(m)}
                       </span>

services/frontend/src/app/(dashboard)/messages/view.tsx

@@ -564,9 +564,18 @@ function MessageDetail({
   return (
     <div className="space-y-3 text-sm">
       <div className="flex items-center gap-3">
-        <Avatar src={m.avatar_url} name={m.username} size={40} />
+        <Avatar
+          src={m.avatar_url}
+          name={m.server_nick ?? m.username}
+          size={40}
+        />
         <div>
-          <div className="font-semibold text-ink">{m.username}</div>
+          <div className="font-semibold text-ink">
+            {m.server_nick ?? m.username}
+          </div>
+          {m.server_nick && m.server_nick !== m.username && (
+            <div className="text-[11px] text-ink-muted">@{m.username}</div>
+          )}
           <div className="mono text-[0.65rem] text-ink-faint">
             {getMessageChannelLabel(m)} · {formatRelativeTime(m.created_at)}
           </div>
@@ -729,12 +738,21 @@ function MessageRow({
           : "border-hairline bg-surface-2 hover:border-hairline-focus hover:bg-surface"
       }`}
     >
-      <Avatar src={m.avatar_url} name={m.username} size={32} />
+      <Avatar
+        src={m.avatar_url}
+        name={m.server_nick ?? m.username}
+        size={32}
+      />
       <div className="min-w-0 flex-1">
         <div className="flex items-center gap-2">
           <span className="truncate text-xs font-semibold text-ink">
-            {m.username}
+            {m.server_nick ?? m.username}
           </span>
+          {m.server_nick && m.server_nick !== m.username && (
+            <span className="truncate font-mono text-[10px] text-ink-muted">
+              @{m.username}
+            </span>
+          )}
           <span className="font-mono text-[10px] text-ink-muted">
             {getMessageChannelLabel(m)}
           </span>

services/frontend/src/lib/types/message.ts

@@ -109,6 +109,8 @@ export interface MessageRecord {
   reference_guild_id?: string | null;
   user_id: string;
   username: string;
+  /** Member's server-specific display name (nickname), from metadata.member.displayName. Falls back to username. */
+  server_nick?: string | null;
   avatar_url?: string | null;
   content: string;
   edited_content?: string | null;