Use Radar Eye logo in the app header + README

- App: top-bar brand mark is now the Radar Eye (drawable/vigil_logo.xml) instead of a generic shield.
- README: centered logo header (docs/logo.png, rendered from docs/logo.svg).
Release 0.1.7.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0187UiEtasyowhEBYs6s9iF5

app/build.gradle.kts

@@ -13,8 +13,8 @@ android {
         applicationId = "org.soulstone.vigil"
         minSdk = 26
         targetSdk = 35
-        versionCode = 7
-        versionName = "0.1.6"
+        versionCode = 8
+        versionName = "0.1.7"
     }
 
     // Fixed debug keystore committed to the repo (a debug key is non-secret — its