fix(gui): say what happens when a network protocol is switched on (UDPFS silent-enable)

Hardware report on Beta-2937: "after turning on udpfs nothing happens, like
it don't even refresh or give any message." The mechanics were all in place
-- applyConfig re-registers the UDPFS tab in-session, and Manual-start tabs
init on a Confirm press inside them -- but NOTHING told the user any of
that: no message fires on enable (the DHCP warning and the restart notice
are conditional), the new tab joins the ring silently, and the block
transports (UDPBD / UDPFS Image) show a tab only once the PC server
answers. From the user's chair: nothing happened.

Add a per-family guidance toast at the moment the protocol changes:
  * UDPFS (Files): open the new UDPFS tab + press Confirm to connect;
    PC side runs udpfsd -d <games folder>.
  * UDPBD / UDPFS (Image): the device tab appears once the PC server
    answers (udpfsd -b / udpbd-server).

Two new lang labels appended at the END of lng_tmpl/_base.yml (append-only
rule; English-only until the lng_fork overlay rerun).

Build-green on ps2dev:latest AND ps2max/dev:v20250725-2; clang-format clean.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Author: NathanNeurotic

lng_tmpl/_base.yml

@@ -917,3 +917,7 @@ gui_strings:
   string: UDPFS Access
 - label: MMCE_GAMEID_NEUTRINO_SKIP
   string: MMCE GameID not applied -- neutrino.elf is on this card (switching it would unload Neutrino).
+- label: NET_UDPFS_TAB_HINT
+  string: UDPFS on -- open the new UDPFS tab and press Confirm to connect. PC side runs udpfsd -d <games folder>.
+- label: NET_UDPBD_TAB_HINT
+  string: Network block device on -- its tab appears once the PC server answers (udpfsd -b for UDPFS Image, udpbd-server for UDPBD).

src/gui.c

@@ -1125,6 +1125,17 @@ void guiShowDeviceConfig(void)
         if (gNetworkProtocol != netProtocolWas && (bdmIsUDPBDLoaded() || ethGetModulesLoaded() || udpfsGetModulesLoaded()))
             guiMsgBox(_l(_STR_NETBOOT_RESTART), 0, NULL);
 
+        // "Nothing happens" guard (hardware report on Beta-2937): enabling a network protocol gave NO
+        // feedback -- the UDPFS tab joins the ring silently and then waits for a Confirm-press inside
+        // it (Manual start), and the block transports show a tab only once the PC server answers.
+        // Tell the user what to expect + which PC server to run, right at the moment they turn it on.
+        if (gNetworkProtocol != netProtocolWas) {
+            if (gNetworkProtocol == NET_PROTO_UDPFS)
+                guiMsgBox(_l(_STR_NET_UDPFS_TAB_HINT), 0, NULL);
+            else if (gNetworkProtocol == NET_PROTO_UDPFSBD || gNetworkProtocol == NET_PROTO_UDPBD)
+                guiMsgBox(_l(_STR_NET_UDPBD_TAB_HINT), 0, NULL);
+        }
+
         // A BDM tab can be latched hidden (bdmNeedsUpdate force-hides it when its enable flag reads 0,
         // then short-circuits until the device generation bumps). Re-evaluate device visibility now so
         // re-enabling a device here brings its tab back without a physical replug.