Add board photos and Home Assistant dashboard screenshot; integrate into README, photos index, changelog

photos/README.md

@@ -1,13 +1,14 @@
-Photographs of the assembled board.
+# Photos
 
-Suggested shots for the README (top-down, evenly lit, plain background, 1600 px wide):
+Photographs of the prototype board (v1). They are embedded in the
+[README](../README.md) and shown in the
+[v1.0.0 release notes](https://git.honney333.work/honney/esp_sensair/releases/tag/v1.0.0).
 
-- `top.jpg`      assembled board, front side, all parts visible
-- `bottom.jpg`   solder side
-- `installed.jpg` board in its final location / enclosure
-- `running.jpg`  Home Assistant dashboard showing live values
-
-Add them to the README once taken:
-
-    ![Assembled board, top](photos/top.jpg)
-    ![Assembled board, bottom](photos/bottom.jpg)
+| File | Description |
+|---|---|
+| `frontside.jpg` | bare fabricated board, front side (straight from the fab) |
+| `backside.jpg` | bare fabricated board, back side (straight from the fab) |
+| `frontside_soldered.jpg` | assembled board, front side, soldered |
+| `backside_soldered.jpg` | assembled board, back side, soldered |
+| `active_co2_measurement.jpg` | board running, active CO₂ measurement |
+| `sensor_current_homeassistant.png` | Home Assistant dashboard with live values |