Scrub location/IP from public assets; add gitleaks pre-commit hook

- README: replace real lat/lon in the config example with 0.0/0.0 and
  drop the city name from the screenshot caption
- viewer screenshot: re-captured with the receiver IP masked
- add .pre-commit-config.yaml running gitleaks to block secrets from
  reaching gitea or the public GitHub mirror

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

.pre-commit-config.yaml

@@ -0,0 +1,14 @@
+# Pre-commit hooks for ADS-Bit.
+#
+# Setup (once):
+#   pip install pre-commit
+#   pre-commit install
+#
+# Thereafter gitleaks scans every commit for secrets (tokens, keys,
+# password hashes) before they can reach gitea or the public GitHub mirror.
+# Run manually across the whole tree with:  pre-commit run --all-files
+repos:
+  - repo: https://github.com/gitleaks/gitleaks
+    rev: v8.18.4
+    hooks:
+      - id: gitleaks

README.md

@@ -10,7 +10,7 @@ A retro SNES-style side-view flight tracker that displays ADS-B aircraft data wi
 
 ### Live viewer
 
-Real-time ADS-B traffic rendered as pixel-art sprites over a directional background — here the East view, with the Las Vegas skyline on the horizon. Aircraft are labelled with callsign, altitude, and distance, and listed in the sidebar sorted by range.
+Real-time ADS-B traffic rendered as pixel-art sprites over a directional background — here the East view, with a desert skyline on the horizon. Aircraft are labelled with callsign, altitude, and distance, and listed in the sidebar sorted by range.
 
 ![Live viewer with aircraft in view](screenshots/viewer.png)