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/proxy/providers/transform.rs

@@ -869,6 +869,34 @@ mod tests {
         assert_eq!(result["usage"]["output_tokens"], 5);
     }
 
+    #[test]
+    fn test_openai_to_anthropic_preserves_id_for_usage_dedup() {
+        let input = json!({
+            "id": "chatcmpl-claude-compatible",
+            "object": "chat.completion",
+            "model": "claude-sonnet-4-5",
+            "choices": [{
+                "index": 0,
+                "message": {"role": "assistant", "content": "Hello!"},
+                "finish_reason": "stop"
+            }],
+            "usage": {"prompt_tokens": 10, "completion_tokens": 5, "total_tokens": 15}
+        });
+
+        let result = openai_to_anthropic(input).unwrap();
+        let usage = crate::proxy::usage::parser::TokenUsage::from_claude_response(&result)
+            .expect("converted Anthropic response should parse usage");
+
+        assert_eq!(
+            usage.message_id.as_deref(),
+            Some("chatcmpl-claude-compatible")
+        );
+        assert_eq!(
+            usage.dedup_request_id(),
+            "session:chatcmpl-claude-compatible"
+        );
+    }
+
     #[test]
     fn test_openai_to_anthropic_with_tool_calls() {
         let input = json!({