docs: add Dashboard/Inventory/Share screenshots to the README

Adds assets/screenshots/{dashboard,inventory,share}.png and a Screenshots section
(Dashboard + Inventory side by side, Share below).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

README.md

@@ -29,6 +29,16 @@ freeze are usually lost. RigDoctor pulls it together and keeps the evidence.
   or share a live **terminal session** for remote help.
 - **Self-updating** — `apt upgrade`, or the in-app updater.
 
+## Screenshots
+
+| Dashboard | Inventory |
+|---|---|
+| ![Dashboard — live sensors](assets/screenshots/dashboard.png) | ![Inventory — hardware/OS](assets/screenshots/inventory.png) |
+
+**Share** — a read-only or interactive terminal session over the relay, for remote help:
+
+![Share — shared terminal session](assets/screenshots/share.png)
+
 ## Install
 
 ### Debian / Ubuntu — `.deb`