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

src/dashboard/usage.rs

@@ -16,7 +16,9 @@ pub(super) async fn handle_usage_summary(State(state): State<DashboardState>) ->
             COUNT(*) as total_requests,
             COALESCE(SUM(total_tokens), 0) as total_tokens,
             COALESCE(SUM(cost), 0.0) as total_cost,
-            COUNT(DISTINCT client_id) as active_clients
+            COUNT(DISTINCT client_id) as active_clients,
+            COALESCE(SUM(cache_read_tokens), 0) as total_cache_read,
+            COALESCE(SUM(cache_write_tokens), 0) as total_cache_write
         FROM llm_requests
         "#,
     )
@@ -64,6 +66,8 @@ pub(super) async fn handle_usage_summary(State(state): State<DashboardState>) ->
             let total_tokens: i64 = t.get("total_tokens");
             let total_cost: f64 = t.get("total_cost");
             let active_clients: i64 = t.get("active_clients");
+            let total_cache_read: i64 = t.get("total_cache_read");
+            let total_cache_write: i64 = t.get("total_cache_write");
 
             let today_requests: i64 = d.get("today_requests");
             let today_cost: f64 = d.get("today_cost");
@@ -87,6 +91,8 @@ pub(super) async fn handle_usage_summary(State(state): State<DashboardState>) ->
                 "today_cost": today_cost,
                 "error_rate": error_rate,
                 "avg_response_time": avg_response_time,
+                "total_cache_read_tokens": total_cache_read,
+                "total_cache_write_tokens": total_cache_write,
             })))
         }
         _ => Json(ApiResponse::error("Failed to fetch usage statistics".to_string())),
@@ -208,7 +214,9 @@ pub(super) async fn handle_providers_usage(
             provider,
             COUNT(*) as requests,
             COALESCE(SUM(total_tokens), 0) as tokens,
-            COALESCE(SUM(cost), 0.0) as cost
+            COALESCE(SUM(cost), 0.0) as cost,
+            COALESCE(SUM(cache_read_tokens), 0) as cache_read,
+            COALESCE(SUM(cache_write_tokens), 0) as cache_write
         FROM llm_requests
         GROUP BY provider
         ORDER BY requests DESC
@@ -226,12 +234,16 @@ pub(super) async fn handle_providers_usage(
                 let requests: i64 = row.get("requests");
                 let tokens: i64 = row.get("tokens");
                 let cost: f64 = row.get("cost");
+                let cache_read: i64 = row.get("cache_read");
+                let cache_write: i64 = row.get("cache_write");
 
                 provider_usage.push(serde_json::json!({
                     "provider": provider,
                     "requests": requests,
                     "tokens": tokens,
                     "cost": cost,
+                    "cache_read_tokens": cache_read,
+                    "cache_write_tokens": cache_write,
                 }));
             }
 
@@ -256,7 +268,9 @@ pub(super) async fn handle_detailed_usage(State(state): State<DashboardState>) -
             model,
             COUNT(*) as requests,
             COALESCE(SUM(total_tokens), 0) as tokens,
-            COALESCE(SUM(cost), 0.0) as cost
+            COALESCE(SUM(cost), 0.0) as cost,
+            COALESCE(SUM(cache_read_tokens), 0) as cache_read,
+            COALESCE(SUM(cache_write_tokens), 0) as cache_write
         FROM llm_requests
         GROUP BY date, client_id, provider, model
         ORDER BY date DESC
@@ -279,6 +293,8 @@ pub(super) async fn handle_detailed_usage(State(state): State<DashboardState>) -
                         "requests": row.get::<i64, _>("requests"),
                         "tokens": row.get::<i64, _>("tokens"),
                         "cost": row.get::<f64, _>("cost"),
+                        "cache_read_tokens": row.get::<i64, _>("cache_read"),
+                        "cache_write_tokens": row.get::<i64, _>("cache_write"),
                     })
                 })
                 .collect();