fix(usage): prevent double-counting between proxy and session-log sources

Proxy writes and session-log sync wrote to proxy_request_logs with
mismatched request_ids: only Claude on a native Anthropic backend used the
shared `session:{message_id}` key. Codex/Gemini and Claude-through-OpenAI
providers always produced distinct ids, so primary-key dedup never fired
and every real request was recorded twice.

Adds a 7-dim fingerprint dedup (app_type, 4 token counts, 2xx status,
model with case-insensitive match, ±10min window) wired into three layers:

- Write path: should_skip_session_insert() blocks duplicate session rows
  before INSERT, unifying the previously-divergent Claude/Codex/Gemini
  paths through a single DedupKey-based helper.
- Read path: effective_usage_log_filter() excludes already-covered session
  rows from every aggregation query.
- Rollup path: same filter applied so usage_daily_rollups never absorbs
  duplicates.

Also adds a covering index (idx_request_logs_dedup_lookup) so the EXISTS
subquery stays index-only, and a transform.rs regression test that pins
openai_to_anthropic id preservation - the missing piece that lets
Claude+OpenAI-compatible providers reuse the session: id scheme.

src-tauri/src/database/schema.rs

@@ -214,6 +214,7 @@ impl Database {
             [],
         )
         .map_err(|e| AppError::Database(e.to_string()))?;
+        Self::create_request_logs_dedup_index_if_supported(conn)?;
 
         // 11. Model Pricing 表
         conn.execute(
@@ -1107,6 +1108,7 @@ impl Database {
                 "data_source",
                 "TEXT NOT NULL DEFAULT 'proxy'",
             )?;
+            Self::create_request_logs_dedup_index_if_supported(conn)?;
         }
 
         // 2. 创建会话日志同步状态表
@@ -1908,6 +1910,36 @@ impl Database {
         Ok(())
     }
 
+    fn create_request_logs_dedup_index_if_supported(conn: &Connection) -> Result<(), AppError> {
+        if !Self::table_exists(conn, "proxy_request_logs")? {
+            return Ok(());
+        }
+
+        let required_columns = [
+            "app_type",
+            "data_source",
+            "input_tokens",
+            "output_tokens",
+            "cache_read_tokens",
+            "created_at",
+            "cache_creation_tokens",
+        ];
+        for column in required_columns {
+            if !Self::has_column(conn, "proxy_request_logs", column)? {
+                return Ok(());
+            }
+        }
+
+        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)",
+            [],
+        )
+        .map_err(|e| AppError::Database(format!("创建使用量去重索引失败: {e}")))?;
+        Ok(())
+    }
+
     fn validate_identifier(s: &str, kind: &str) -> Result<(), AppError> {
         if s.is_empty() {
             return Err(AppError::Database(format!("{kind} 不能为空")));