fix: IRC SPA cleanup — /motd, /query, Firefox / key, default MOTD

- Add default MOTD with figlet-style ASCII art for neoirc
- Add MOTD server command so /motd can be re-requested
- Add /motd client command to display message of the day
- Add /query command to open DM tabs with optional message
- Add /clear command to clear messages in current tab
- Fix Firefox quick search conflict: global keydown handler
  captures '/' and redirects focus to the input element
- Auto-focus input on SPA init and tab changes
- Show MOTD on resumed sessions (new sessions get it from
  server automatically during creation)
- Update /help with new commands
- Style MOTD on login screen for better ASCII art display

web/src/style.css

@@ -70,14 +70,14 @@ body,
 }
 
 .login-box .motd {
-  color: var(--text-dim);
-  font-size: 12px;
+  color: var(--accent);
+  font-size: 11px;
   margin-bottom: 20px;
   text-align: left;
-  white-space: pre-wrap;
+  white-space: pre;
   font-family: inherit;
-  border-left: 2px solid var(--border);
-  padding-left: 12px;
+  line-height: 1.2;
+  overflow-x: auto;
 }
 
 .login-box form {