Add README screenshots: staged in-game captures between description and Downloads

- New capture tool src/test/capture_screenshots.gd (windowed, staged:
  venue overview, targeting an NPC, access inspection, radio report)
- Generated shots saved to docs/screenshots/ and embedded as a 2x2 gallery
  in README above the Downloads section

README.md

@@ -6,6 +6,15 @@ The central design goal is simple:
 
 > The player wins by choosing the lowest level of escalation that keeps everyone safe.
 
+## Screenshots
+
+| | |
+|---|---|
+| ![Venue overview: the Hollywood Boulevard entrance with steps, sidewalk, and restricted door](docs/screenshots/01-venue-overview.png) | ![Targeting an approaching NPC with the interaction HUD](docs/screenshots/02-targeting-npc.png) |
+| ![Access inspection: wristband/credential check with allow/deny prompt](docs/screenshots/03-access-inspection.png) | ![Radio report form: emergency dispatch panel](docs/screenshots/04-radio-report.png) |
+
+*Screenshots are generated by [`src/test/capture_screenshots.gd`](src/test/capture_screenshots.gd) from the current build.*
+
 ## ⬇️ Downloads
 
 | Platform | Package |