Admin Messages: CSV export of the whole filtered list

A right-aligned 'Export CSV ↓' link in the filter row downloads /_gm/messages.csv
with the active filters (game / sender / name / ext masks), exporting every matching
message (capped at 100k) regardless of the page window — columns time, source,
sender_id, sender, ip, message, game_id.

backend/internal/adminconsole/assets/console.css

@@ -74,6 +74,7 @@ h1 { font-size: 1.4rem; margin: 0 0 0.4rem; }
 .subnav a.active { color: var(--ink); }
 
 .form { display: flex; flex-wrap: wrap; gap: 0.6rem; align-items: end; margin-top: 0.4rem; }
+.form .export { margin-left: auto; align-self: center; color: var(--accent); white-space: nowrap; }
 .form.col { flex-direction: column; align-items: stretch; max-width: 540px; }
 .form label { display: flex; flex-direction: column; gap: 0.2rem; font-size: 0.85rem; color: var(--ink-dim); }
 .form input, .form select, .form textarea {

backend/internal/adminconsole/templates/pages/messages.gohtml

@@ -7,6 +7,7 @@
 <input name="name" value="{{.NameMask}}" placeholder="sender name mask (* ?)">
 <input name="ext" value="{{.ExtMask}}" placeholder="sender external id mask (* ?)">
 <button type="submit">Filter</button>
+<a class="export" href="/_gm/messages.csv?{{.FilterQuery}}">Export CSV ↓</a>
 </form>
 {{if or .GameID .UserID}}
 <p class="note">Filtered{{if .GameID}} to game <a href="/_gm/games/{{.GameID}}">{{.GameID}}</a>{{end}}{{if .UserID}} from <a href="/_gm/users/{{.UserID}}">sender</a>{{end}} · <a href="/_gm/messages">clear</a></p>