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/src/routes/signup/+page.svelte

@@ -45,7 +45,7 @@
 								<!-- Header -->
 								<div class="text-center mb-8">
 									<div class="mb-4">
-										<h1 class="text-3xl font-bold text-primary mb-1">AdventureLog</h1>
+										<h1 class="text-3xl font-bold text-primary mb-1">Voyage</h1>
 										<div class="w-12 h-1 bg-primary mx-auto rounded"></div>
 									</div>
 									<h2 class="text-4xl font-bold text-base-content mb-2">{$t('auth.signup')}</h2>
@@ -247,10 +247,10 @@
 </div>
 
 <svelte:head>
-	<title>Sign Up | AdventureLog</title>
+	<title>Sign Up | Voyage</title>
 	<meta
 		name="description"
-		content="Sign up for AdventureLog to explore the world and document your adventures!"
+		content="Sign up for Voyage to explore the world and document your adventures!"
 	/>
 </svelte:head>