Rename AdventureLog to Voyage and add fork attribution

- Replace all AdventureLog references with Voyage across ~102 files
  (7 case variants: AdventureLog, adventurelog, Adventurelog, ADVENTURELOG,
  AdventUrelog, AdventureLOG, adventure-log, adventure_log)
- Rename brand, static, and documentation assets to use voyage naming
- Rename install_adventurelog.sh → install_voyage.sh
- Update README.md and voyage_overview.md to credit AdventureLog as
  the upstream project and Sean Morley as its original creator

frontend/static/manifest.json

@@ -1,10 +1,10 @@
 {
-	"short_name": "AdventureLog",
-	"name": "AdventureLog",
+	"short_name": "Voyage",
+	"name": "Voyage",
 	"start_url": "/dashboard",
 	"icons": [
 		{
-			"src": "adventurelog.svg",
+			"src": "voyage.svg",
 			"type": "image/svg+xml",
 			"sizes": "any"
 		}