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

backend/server/templates/home.html

@@ -1,7 +1,7 @@
 {% extends "base.html" %} {% block content %}
 <!-- Main jumbotron for a primary marketing message or call to action -->
 <div class="jumbotron">
-  <h1>AdventureLog API Server</h1>
+  <h1>Voyage API Server</h1>
   <p>
     <a class="btn btn-primary btn-lg" href="/admin" role="button">Admin Site</a>
     <a