docs: document the Room Server role

- README: add Room Server to "Device Roles" + a build command in "Building"
- ARCHITECTURE.md: role list two -> four (add Room Server + the
  previously-undocumented Observer)
- Repeater_CLI_commands.md: note the room server shares this CLI
- boards/example_board/README.md: add the room_server.conf build snippet

zephcore/ARCHITECTURE.md

@@ -25,10 +25,12 @@
 
 ## 1. Project Overview
 
-ZephCore is a LoRa mesh networking firmware running on Zephyr RTOS. It supports two device roles:
+ZephCore is a LoRa mesh networking firmware running on Zephyr RTOS. It supports four device roles:
 
 - **Companion**: BLE-connected device paired with a phone app. Full contact/channel/message management.
 - **Repeater**: Autonomous headless relay node. CLI administration via authenticated mesh connections or serial UART.
+- **Room Server**: Headless store-and-forward shared message room (BBS). Reuses the repeater's ACL/region/CLI; pushes new posts to logged-in clients (per-client sync cursor + ACK).
+- **Observer** (ESP32): Listen-only node that publishes received LoRa packets to MQTT over WiFi.
 
 Supported hardware: nRF52840, nRF54L15, ESP32-C3/C6/S3, EFR32MG24 — all with SX1262 or LR1110 LoRa radios.
 

zephcore/Repeater_CLI_commands.md

@@ -2,6 +2,8 @@
 
 All commands are sent over USB serial (CDC-ACM). Commands sent remotely over the mesh (non-zero `sender_timestamp`) cannot access USB-only commands.
 
+> The **Room Server** role shares this CLI — the common commands (radio, region, password, advert, gps, etc.) plus `setperm` / `get acl` all apply.
+
 **Sources:**
 - `helpers/CommonCLI.cpp` — common commands shared by all roles
 - `app/RepeaterMesh.cpp` — repeater-specific commands

zephcore/boards/example_board/README.md

@@ -113,6 +113,14 @@ Append `-- -DEXTRA_CONF_FILE="boards/common/repeater.conf"` to any build command
 west build -b rak4631 zephcore -- -DEXTRA_CONF_FILE="boards/common/repeater.conf"
 ```
 
+### Building for Room Server Role
+
+Append `-- -DEXTRA_CONF_FILE="boards/common/room_server.conf"` to any build command:
+
+```
+west build -b rak4631 zephcore -- -DEXTRA_CONF_FILE="boards/common/room_server.conf"
+```
+
 ### Production Build (logging disabled)
 
 ```