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  subqueries use index lookup instead of full scan; drop superseded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/commands/usage.rs

@@ -220,6 +220,19 @@ pub fn sync_session_usage(
         }
     }
 
+    // 同步 Hermes 使用数据
+    match crate::services::session_usage_hermes::sync_hermes_usage(&state.db) {
+        Ok(hermes_result) => {
+            result.imported += hermes_result.imported;
+            result.skipped += hermes_result.skipped;
+            result.files_scanned += hermes_result.files_scanned;
+            result.errors.extend(hermes_result.errors);
+        }
+        Err(e) => {
+            result.errors.push(format!("Hermes 同步失败: {e}"));
+        }
+    }
+
     Ok(result)
 }