feat: add cache token tracking and cache-aware cost calculation

Track cache_read_tokens and cache_write_tokens end-to-end: parse from
provider responses (OpenAI, DeepSeek, Grok, Gemini), persist to SQLite,
apply cache-aware pricing from the model registry, and surface in API
responses and the dashboard.

- Add cache fields to ProviderResponse, StreamUsage, RequestLog structs
- Parse cached_tokens (OpenAI/Grok), prompt_cache_hit/miss (DeepSeek),
  cachedContentTokenCount (Gemini) from provider responses
- Send stream_options.include_usage for streaming; capture real usage
  from final SSE chunk in AggregatingStream
- ALTER TABLE migration for cache_read_tokens/cache_write_tokens columns
- Cache-aware cost formula using registry cache_read/cache_write rates
- Update Provider trait calculate_cost signature across all providers
- Add cache_read_tokens/cache_write_tokens to Usage API response
- Dashboard: cache hit rate card, cache columns in pricing and usage
  tables, cache token aggregation in SQL queries
- Remove API debug panel and verbose console logging from api.js
- Bump static asset cache-bust to v5

static/js/pages/costs.js

@@ -31,7 +31,10 @@ class CostsPage {
                 avgDailyCost: data.total_cost / 30, // Simplified
                 costTrend: 5.2,
                 budgetUsed: Math.min(Math.round((data.total_cost / 100) * 100), 100), // Assuming $100 budget
-                projectedMonthEnd: data.today_cost * 30
+                projectedMonthEnd: data.today_cost * 30,
+                cacheReadTokens: data.total_cache_read_tokens || 0,
+                cacheWriteTokens: data.total_cache_write_tokens || 0,
+                totalTokens: data.total_tokens || 0,
             };
             
             this.renderCostStats();
@@ -44,6 +47,10 @@ class CostsPage {
     renderCostStats() {
         const container = document.getElementById('cost-stats');
         if (!container) return;
+
+        const cacheHitRate = this.costData.totalTokens > 0
+            ? ((this.costData.cacheReadTokens / this.costData.totalTokens) * 100).toFixed(1)
+            : '0.0';
         
         container.innerHTML = `
             <div class="stat-card">
@@ -74,6 +81,19 @@ class CostsPage {
                 </div>
             </div>
             
+            <div class="stat-card">
+                <div class="stat-icon primary">
+                    <i class="fas fa-bolt"></i>
+                </div>
+                <div class="stat-content">
+                    <div class="stat-value">${cacheHitRate}%</div>
+                    <div class="stat-label">Cache Hit Rate</div>
+                    <div class="stat-change">
+                        ${window.api.formatNumber(this.costData.cacheReadTokens)} cached tokens
+                    </div>
+                </div>
+            </div>
+            
             <div class="stat-card">
                 <div class="stat-icon danger">
                     <i class="fas fa-piggy-bank"></i>
@@ -181,15 +201,24 @@ class CostsPage {
         const tableBody = document.querySelector('#pricing-table tbody');
         if (!tableBody) return;
         
-        tableBody.innerHTML = data.map(row => `
-            <tr>
-                <td><span class="badge-client">${row.provider.toUpperCase()}</span></td>
-                <td><code class="code-sm">${row.id}</code></td>
-                <td>${window.api.formatCurrency(row.prompt_cost)} / 1M</td>
-                <td>${window.api.formatCurrency(row.completion_cost)} / 1M</td>
-                <td>Now</td>
-            </tr>
-        `).join('');
+        tableBody.innerHTML = data.map(row => {
+            const cacheRead = row.cache_read_cost != null
+                ? `${window.api.formatCurrency(row.cache_read_cost)} / 1M`
+                : '<span style="color:var(--fg4)">--</span>';
+            const cacheWrite = row.cache_write_cost != null
+                ? `${window.api.formatCurrency(row.cache_write_cost)} / 1M`
+                : '<span style="color:var(--fg4)">--</span>';
+            return `
+                <tr>
+                    <td><span class="badge-client">${row.provider.toUpperCase()}</span></td>
+                    <td><code class="code-sm">${row.id}</code></td>
+                    <td>${window.api.formatCurrency(row.prompt_cost)} / 1M</td>
+                    <td>${window.api.formatCurrency(row.completion_cost)} / 1M</td>
+                    <td>${cacheRead}</td>
+                    <td>${cacheWrite}</td>
+                </tr>
+            `;
+        }).join('');
     }
 
     setupEventListeners() {