Stage 17 round 6 (#18, PR D): admin Messages moderation section

A new /_gm/messages console page lists posted chat messages (nudges
excluded) newest-first — time, source (guest/robot/oldest identity kind),
sender (linked to the user card), IP, body, game (linked to the game card)
— searchable by sender name / external-id glob masks and pinnable to one
game (?game=) or sender (?user=), linked from the game and user cards.

The list query lives in social (raw SQL, kind='message', source via a SQL
CASE), reusing the now-exported account.LikePattern. Server-rendered
adminconsole MessagesView + messages.gohtml, 50/page via the shared pager.

Tests: adminconsole render case; backend integration AdminListMessages
(real Postgres) — nudge exclusion, game/sender pins, glob masks, source.
Docs: ARCHITECTURE section 8 chat moderation, PLAN round-6.

backend/internal/adminconsole/views.go

@@ -73,6 +73,32 @@ type UserRow struct {
 	MoveMax      string
 }
 
+// MessagesView is the paginated chat-message moderation list. NameMask/ExtMask are the
+// current sender glob filters; GameID/UserID pin the list to one game / sender (set from a
+// game or user card); FilterQuery is the active filters encoded for the pager links.
+type MessagesView struct {
+	Items       []MessageRow
+	Pager       Pager
+	NameMask    string
+	ExtMask     string
+	GameID      string
+	UserID      string
+	FilterQuery string
+}
+
+// MessageRow is one chat message in the moderation list: its sender (linked to the user
+// card), source, IP, body, game (linked to the game card) and time.
+type MessageRow struct {
+	ID         string
+	SenderID   string
+	SenderName string
+	Source     string
+	IP         string
+	Body       string
+	GameID     string
+	CreatedAt  string
+}
+
 // UserDetailView is one account with its stats, identities and recent games.
 type UserDetailView struct {
 	ID                     string