fix(repeater/sensor/room_server/secure_chat cli): permanent lockup without CR

The buffer-full branch writes the forced '\r' to command[sizeof-1], but the
line-complete check below tests command[len-1] (== sizeof-2 when the buffer
is full), so the line never completes: the read loop's condition
(len < sizeof-1) stays false forever and the CLI stops reading serial input
until reboot. Writing at [sizeof-1] also overwrites the string's NUL
terminator, so the next strlen() reads past the buffer (UB).

Write the '\r' at command[sizeof-2] instead — exactly the position the
completion check tests. The overflowed input is then processed as an
(unknown) command, the buffer resets, and the CLI keeps working.

Reproduced on hardware (T1000-E repeater): ~53 arrow-key presses in an
attached terminal (3-byte ESC[A escape sequences, 159 bytes with no CR)
filled the buffer and the CLI never accepted a command again until reboot.

The same copy-pasted pattern is fixed in simple_repeater, simple_sensor,
simple_room_server and simple_secure_chat.

examples/simple_repeater/main.cpp

@@ -135,7 +135,7 @@ void loop() {
     if (c == '\r') break;
   }
   if (len == sizeof(command)-1) {  // command buffer full
-    command[sizeof(command)-1] = '\r';
+    command[sizeof(command)-2] = '\r';   // force-complete the line ([len-1] is tested below; [sizeof-1] would clobber the NUL and never match)
   }
 
   if (len > 0 && command[len - 1] == '\r') {  // received complete line

examples/simple_room_server/main.cpp

@@ -114,7 +114,7 @@ void loop() {
     Serial.print(c);
   }
   if (len == sizeof(command)-1) {  // command buffer full
-    command[sizeof(command)-1] = '\r';
+    command[sizeof(command)-2] = '\r';   // force-complete the line ([len-1] is tested below; [sizeof-1] would clobber the NUL and never match)
   }
 
   if (len > 0 && command[len - 1] == '\r') {  // received complete line

examples/simple_secure_chat/main.cpp

@@ -535,7 +535,7 @@ public:
       Serial.print(c);
     }
     if (len == sizeof(command)-1) {  // command buffer full
-      command[sizeof(command)-1] = '\r';
+      command[sizeof(command)-2] = '\r';   // force-complete the line ([len-1] is tested below; [sizeof-1] would clobber the NUL and never match)
     }
 
     if (len > 0 && command[len - 1] == '\r') {  // received complete line

examples/simple_sensor/main.cpp

@@ -131,7 +131,7 @@ void loop() {
     Serial.print(c);
   }
   if (len == sizeof(command)-1) {  // command buffer full
-    command[sizeof(command)-1] = '\r';
+    command[sizeof(command)-2] = '\r';   // force-complete the line ([len-1] is tested below; [sizeof-1] would clobber the NUL and never match)
   }
 
   if (len > 0 && command[len - 1] == '\r') {  // received complete line