feat: wifi companion configuration via cli rescue

The idea with this was allowing users to use WiFi companions,
without having to compile a build. This change enables CLI
Rescue commands to companion wifi builds so they
can be provisioned via USB cable. (The CLI is limited
in number of characters, so some longer SSIDs would still have
to be compiled in, for now.)

This would also allow a wifi companion firmware to be available
for download from the MeshCore site and while the user is setting
up, they could provision their SSID/password on the web-CLI or
a local terminal via USB without having to compile a build.

Longer-term, other solutions could be devised to make this more
flexible, like the mobile app could add in the wifi provisioning
step with a Bluetooth bootstrap stage, leveraging this code as
the mechanism to store/configure.

CLI Rescue commands added:

| Command | Syntax | Description |
|---|---|---|
| Set WiFi SSID | `wifi_ssid <ssid>` | Set the network name |
| Set WiFi Password | `wifi_pwd <pwd>` | Set the network password |
| Commit WiFi Settings | `wifi_commit` | Apply and save settings |
| Clear WiFi Settings | `wifi_clear` | Reset all WiFi settings |

This is dependent on [PR 2706](https://github.com/meshcore-dev/MeshCore/pull/2706).

Tested on Heltec v3

examples/companion_radio/MyMesh.cpp

@@ -2004,9 +2004,17 @@ void MyMesh::enterCLIRescue() {
   _cli_rescue = true;
   cli_command[0] = 0;
   Serial.println("========= CLI Rescue =========");
+  Serial.println("Commands: set pin <n>, rebuild, erase, reboot, ls, cat, rm");
+#ifdef WIFI_SSID
+  Serial.println("WiFi:     wifi_ssid <ssid>, wifi_pwd <pwd>, wifi_commit, wifi_clear");
+#endif
 }
 
 void MyMesh::checkCLIRescueCmd() {
+#ifdef WIFI_SSID
+  static char staged_ssid[33] = {0};
+  static char staged_pwd[65]  = {0};
+#endif
   int len = strlen(cli_command);
   while (Serial.available() && len < sizeof(cli_command)-1) {
     char c = Serial.read();
@@ -2168,6 +2176,42 @@ void MyMesh::checkCLIRescueCmd() {
 
       }
 
+#ifdef WIFI_SSID
+    } else if (memcmp(cli_command, "wifi_ssid ", 10) == 0) {
+      strncpy(staged_ssid, &cli_command[10], sizeof(staged_ssid) - 1);
+      staged_ssid[sizeof(staged_ssid) - 1] = 0;
+      Serial.printf("  > SSID staged: \"%s\" (not saved yet, use wifi_commit)\n", staged_ssid);
+    } else if (memcmp(cli_command, "wifi_pwd ", 9) == 0) {
+      strncpy(staged_pwd, &cli_command[9], sizeof(staged_pwd) - 1);
+      staged_pwd[sizeof(staged_pwd) - 1] = 0;
+      Serial.println("  > Password staged (not saved yet, use wifi_commit)");
+    } else if (strcmp(cli_command, "wifi_commit") == 0) {
+      if (staged_ssid[0] == 0 || staged_pwd[0] == 0) {
+        Serial.println("  Error: stage both wifi_ssid and wifi_pwd before committing");
+      } else {
+        File f = _store->getPrimaryFS()->open("/wifi_config", "w", true);
+        if (f) {
+          f.print(staged_ssid); f.print('\n');
+          f.print(staged_pwd);  f.print('\n');
+          f.close();
+          Serial.printf("  > Saved SSID \"%s\" to flash, rebooting...\n", staged_ssid);
+          board.reboot();
+        } else {
+          Serial.println("  Error: failed to write /wifi_config");
+        }
+      }
+    } else if (strcmp(cli_command, "wifi_clear") == 0) {
+      _store->getPrimaryFS()->remove("/wifi_config");
+      Serial.println("  > /wifi_config removed, using compiled-in defaults on next boot, rebooting...");
+      board.reboot();
+    } else if (strcmp(cli_command, "wifi_show") == 0) {
+      Serial.printf("  Staged SSID: \"%s\"\n", staged_ssid[0] ? staged_ssid : "(none)");
+      Serial.printf("  Staged PWD:  %s\n",     staged_pwd[0] ? "(set)"    : "(none)");
+      bool has_config = _store->getPrimaryFS()->exists("/wifi_config");
+      Serial.printf("  /wifi_config on flash: %s\n", has_config ? "yes" : "no (using compiled-in defaults)");
+#endif
+
+
     } else if (strcmp(cli_command, "reboot") == 0) {
       board.reboot();  // doesn't return
     } else {