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/api.js

@@ -17,61 +17,25 @@ class ApiClient {
             headers['Authorization'] = `Bearer ${window.authManager.token}`;
         }
 
+        const response = await fetch(url, {
+            ...options,
+            headers
+        });
+
+        const text = await response.text();
+
+        let result;
         try {
-            console.log(`[API] Fetching ${url}...`);
-            const response = await fetch(url, {
-                ...options,
-                headers
-            });
-
-            console.log(`[API] ${url} → status=${response.status} ok=${response.ok} type=${response.headers.get('content-type')}`);
-
-            const text = await response.text();
-            console.log(`[API] ${url} → body length=${text.length}, first 200 chars:`, text.substring(0, 200));
-
-            let result;
-            try {
-                result = JSON.parse(text);
-            } catch (parseErr) {
-                const msg = `JSON parse failed for ${url}: ${parseErr.message}. Body: ${text.substring(0, 300)}`;
-                console.error(`[API] ${msg}`);
-                this._addDebugEntry(url, 'JSON_PARSE_ERROR', msg);
-                throw new Error(msg);
-            }
-
-            if (!response.ok || !result.success) {
-                const msg = `API error for ${url}: ok=${response.ok} success=${result.success} error=${result.error} status=${response.status}`;
-                console.error(`[API] ${msg}`);
-                this._addDebugEntry(url, 'API_ERROR', msg);
-                throw new Error(result.error || `HTTP error! status: ${response.status}`);
-            }
-
-            console.log(`[API] ${url} → SUCCESS, data keys:`, result.data ? Object.keys(result.data) : 'null');
-            return result.data;
-        } catch (error) {
-            console.error(`[API] Request failed (${path}):`, error);
-            this._addDebugEntry(url, 'EXCEPTION', error.message);
-            throw error;
+            result = JSON.parse(text);
+        } catch (parseErr) {
+            throw new Error(`JSON parse failed for ${url}: ${parseErr.message}`);
         }
-    }
 
-    // Visible on-page debug panel for diagnosing fetch failures
-    _addDebugEntry(url, status, detail) {
-        let panel = document.getElementById('api-debug-panel');
-        if (!panel) {
-            panel = document.createElement('div');
-            panel.id = 'api-debug-panel';
-            panel.style.cssText = 'position:fixed;bottom:0;left:0;right:0;max-height:200px;overflow-y:auto;background:#1d2021;color:#fbf1c7;font-family:monospace;font-size:11px;padding:8px;z-index:99999;border-top:2px solid #cc241d;';
-            const title = document.createElement('div');
-            title.style.cssText = 'font-weight:bold;margin-bottom:4px;color:#fb4934;';
-            title.textContent = 'API Debug Panel (remove after fixing)';
-            panel.appendChild(title);
-            document.body.appendChild(panel);
+        if (!response.ok || !result.success) {
+            throw new Error(result.error || `HTTP error! status: ${response.status}`);
         }
-        const entry = document.createElement('div');
-        entry.style.cssText = 'margin:2px 0;padding:2px 4px;background:#282828;border-left:3px solid ' + (status === 'EXCEPTION' ? '#fb4934' : '#fabd2f') + ';';
-        entry.textContent = `[${status}] ${url}: ${detail}`;
-        panel.appendChild(entry);
+
+        return result.data;
     }
 
     async get(path) {