feat(usage): add Hermes Agent tracking + fix zero-cost bug + perf

Hermes:
- Parse ~/.hermes/state.db sessions (incl. profiles/*/state.db) into
  proxy_request_logs with data_source='hermes_session', WAL-aware
  incremental sync, Hermes-reported cost preferred over model_pricing
  fallback

Zero-cost bug (dashboard showed \$0 totals):
- GPT-5.5 family default pricing (~83% of affected rows used GPT-5.5)
- find_model_pricing_row: ASCII-lowercase normalization so
  "OpenAI/GPT-5.5@HIGH" matches seeded "gpt-5.5"
- Startup cost backfill in async task: scan rows where total_cost <= 0
  but tokens > 0, recompute via model_pricing in a single transaction

Performance:
- Add (app_type, created_at DESC) covering index for dashboard range
  queries
- Add expression index on COALESCE(data_source, 'proxy') so dedup EXISTS
  subqueries use index lookup instead of full scan; drop superseded
  idx_request_logs_dedup_lookup

Refactor:
- row_to_request_log_detail helper (3-way de-dup; fixes cost_multiplier
  \"1\" vs \"1.0\" drift between callers)
- Promote get_sync_state/update_sync_state to shared session_usage
  module (4 copies -> 1)
- run_step helper in lib.rs replaces 9 if-let-Err blocks
- maybe_backfill_log_costs returns bool to skip duplicate total_cost
  parsing in caller

src-tauri/src/database/schema.rs

@@ -214,7 +214,7 @@ impl Database {
             [],
         )
         .map_err(|e| AppError::Database(e.to_string()))?;
-        Self::create_request_logs_dedup_index_if_supported(conn)?;
+        Self::create_request_logs_usage_indexes_if_supported(conn)?;
 
         // 11. Model Pricing 表
         conn.execute(
@@ -1108,7 +1108,7 @@ impl Database {
                 "data_source",
                 "TEXT NOT NULL DEFAULT 'proxy'",
             )?;
-            Self::create_request_logs_dedup_index_if_supported(conn)?;
+            Self::create_request_logs_usage_indexes_if_supported(conn)?;
         }
 
         // 2. 创建会话日志同步状态表
@@ -1298,6 +1298,13 @@ impl Database {
                 "0.30",
                 "3.75",
             ),
+            // GPT-5.5 系列
+            ("gpt-5.5", "GPT-5.5", "5", "30", "0.50", "0"),
+            ("gpt-5.5-low", "GPT-5.5", "5", "30", "0.50", "0"),
+            ("gpt-5.5-medium", "GPT-5.5", "5", "30", "0.50", "0"),
+            ("gpt-5.5-high", "GPT-5.5", "5", "30", "0.50", "0"),
+            ("gpt-5.5-xhigh", "GPT-5.5", "5", "30", "0.50", "0"),
+            ("gpt-5.5-minimal", "GPT-5.5", "5", "30", "0.50", "0"),
             // GPT-5.4 系列
             ("gpt-5.4", "GPT-5.4", "2.50", "15", "0.25", "0"),
             ("gpt-5.4-mini", "GPT-5.4 Mini", "0.75", "4.50", "0.075", "0"),
@@ -1910,11 +1917,22 @@ impl Database {
         Ok(())
     }
 
-    fn create_request_logs_dedup_index_if_supported(conn: &Connection) -> Result<(), AppError> {
+    fn create_request_logs_usage_indexes_if_supported(conn: &Connection) -> Result<(), AppError> {
         if !Self::table_exists(conn, "proxy_request_logs")? {
             return Ok(());
         }
 
+        let has_app_type = Self::has_column(conn, "proxy_request_logs", "app_type")?;
+        let has_created_at = Self::has_column(conn, "proxy_request_logs", "created_at")?;
+        if has_app_type && has_created_at {
+            conn.execute(
+                "CREATE INDEX IF NOT EXISTS idx_request_logs_app_created_at
+                 ON proxy_request_logs(app_type, created_at DESC)",
+                [],
+            )
+            .map_err(|e| AppError::Database(format!("创建使用量应用时间索引失败: {e}")))?;
+        }
+
         let required_columns = [
             "app_type",
             "data_source",
@@ -1930,13 +1948,20 @@ impl Database {
             }
         }
 
+        conn.execute("DROP INDEX IF EXISTS idx_request_logs_dedup_lookup", [])
+            .map_err(|e| AppError::Database(format!("删除旧使用量去重索引失败: {e}")))?;
+
+        // 查询层为了兼容历史 NULL data_source 行，会使用
+        // COALESCE(data_source, 'proxy')。普通 data_source 索引无法匹配该表达式，
+        // 会让跨源去重子查询退化成大量扫描；表达式索引让 SQLite 能按同一表达式查找。
         conn.execute(
-            "CREATE INDEX IF NOT EXISTS idx_request_logs_dedup_lookup
-             ON proxy_request_logs(app_type, data_source, input_tokens, output_tokens,
-                                   cache_read_tokens, created_at, cache_creation_tokens)",
+            "CREATE INDEX IF NOT EXISTS idx_request_logs_dedup_lookup_expr
+             ON proxy_request_logs(app_type, COALESCE(data_source, 'proxy'), input_tokens,
+                                   output_tokens, cache_read_tokens, created_at,
+                                   cache_creation_tokens)",
             [],
         )
-        .map_err(|e| AppError::Database(format!("创建使用量去重索引失败: {e}")))?;
+        .map_err(|e| AppError::Database(format!("创建使用量去重表达式索引失败: {e}")))?;
         Ok(())
     }