feat(account): display OpenRouter usage on account page

Show cumulative cost, API call count, and total tokens in card
layout when the user has AI usage data.

src/application/routes/account.rs

@@ -16,6 +16,36 @@ use super::auth::is_authenticated;
 
 // --- View types ---
 
+#[derive(Serialize)]
+pub struct AiUsageView {
+    pub total_calls: i64,
+    pub total_tokens: String,
+    pub total_cost: String,
+}
+
+fn format_cost(cost: f64) -> String {
+    if cost < 0.01 {
+        format!("${cost:.4}")
+    } else {
+        format!("${cost:.2}")
+    }
+}
+
+fn format_number(n: i64) -> String {
+    if n < 1_000 {
+        return n.to_string();
+    }
+    let s = n.to_string();
+    let mut result = String::with_capacity(s.len() + s.len() / 3);
+    for (i, c) in s.chars().rev().enumerate() {
+        if i > 0 && i % 3 == 0 {
+            result.push(',');
+        }
+        result.push(c);
+    }
+    result.chars().rev().collect()
+}
+
 #[derive(Serialize)]
 pub struct PasskeyView {
     pub id: i64,
@@ -43,6 +73,7 @@ fn format_date(dt: DateTime<Utc>) -> String {
 struct AccountTemplate {
     nav_active: &'static str,
     is_authenticated: bool,
+    ai_usage: Option<AiUsageView>,
     passkeys: Vec<PasskeyView>,
     tokens: Vec<TokenView>,
 }
@@ -91,9 +122,22 @@ pub(crate) async fn account_page(
         })
         .collect();
 
+    let ai_usage = state
+        .ai_usage_repo
+        .summary_for_user(auth_user.id)
+        .await
+        .ok()
+        .filter(|s| s.total_calls > 0)
+        .map(|s| AiUsageView {
+            total_calls: s.total_calls,
+            total_tokens: format_number(s.total_tokens),
+            total_cost: format_cost(s.total_cost),
+        });
+
     let template = AccountTemplate {
         nav_active: "account",
         is_authenticated: true,
+        ai_usage,
         passkeys,
         tokens,
     };

templates/account.html

@@ -212,6 +212,27 @@
   <div id="backup-error" class="mt-3 hidden rounded-md bg-red-100 border border-red-300 p-3 text-sm text-red-800"></div>
 </section>
 
+<!-- OpenRouter Usage -->
+{% if let Some(usage) = ai_usage %}
+<section>
+  <h2 class="text-lg font-semibold text-amber-700 mb-3">OpenRouter Usage</h2>
+  <div class="grid grid-cols-1 md:grid-cols-3 gap-3">
+    <div class="rounded-lg border border-amber-200 bg-amber-50 px-4 pt-4 pb-3 shadow-sm">
+      <span class="block text-sm text-stone-500">Total Cost</span>
+      <span class="mt-1 block text-lg font-semibold text-amber-800">{{ usage.total_cost }}</span>
+    </div>
+    <div class="rounded-lg border border-amber-200 bg-amber-50 px-4 pt-4 pb-3 shadow-sm">
+      <span class="block text-sm text-stone-500">API Calls</span>
+      <span class="mt-1 block text-lg font-semibold text-amber-800">{{ usage.total_calls }}</span>
+    </div>
+    <div class="rounded-lg border border-amber-200 bg-amber-50 px-4 pt-4 pb-3 shadow-sm">
+      <span class="block text-sm text-stone-500">Total Tokens</span>
+      <span class="mt-1 block text-lg font-semibold text-amber-800">{{ usage.total_tokens }}</span>
+    </div>
+  </div>
+</section>
+{% endif %}
+
 <!-- Sign Out -->
 <section>
   <form method="post" action="/logout">