fix(relay): audit fixes — abort signal, model selector guard, SSE CRLF, SQL format

Addresses findings from deep code audit:

H-1: Pass abortController.signal to saasClient.chatCompletion() so
     user-cancelled streams actually abort the HTTP connection (was only
     stopping the read loop, leaving server-side SSE connection open).

H-2: ModelSelector now shows only when (!isTauriRuntime() || isLoggedIn).
     Prevents decorative model list in Tauri local kernel mode where model
     selection has no effect (violates CLAUDE.md §5.2).

M-1: Normalize CRLF to LF before SSE event boundary parsing (\n\n).
     Prevents buffer overflow when behind nginx/CDN with CRLF line endings.

M-2: SQL window_minute comparison uses to_char(NOW()-interval, format)
     instead of (NOW()-interval)::TEXT, matching the stored format exactly.

M-3: sort_candidates_by_quota uses same sliding 60s window as select_best_key.

LOW: Fix misleading invalidate_cache doc comment.

crates/zclaw-saas/src/relay/key_pool.rs

@@ -28,7 +28,7 @@ fn get_cache() -> &'static DashMap<String, CachedSelection> {
     KEY_SELECTION_CACHE.get_or_init(DashMap::new)
 }
 
-/// Invalidate cached selection for a provider (called on usage record and 429 marking)
+/// Invalidate cached selection for a provider (called on 429 marking)
 fn invalidate_cache(provider_id: &str) {
     let cache = get_cache();
     cache.remove(provider_id);
@@ -86,7 +86,7 @@ pub async fn select_best_key(db: &PgPool, provider_id: &str, enc_key: &[u8; 32])
                     COALESCE(SUM(uw.token_count), 0)
              FROM provider_keys pk
              LEFT JOIN key_usage_window uw ON pk.id = uw.key_id
-               AND uw.window_minute >= (NOW() - INTERVAL '1 minute')::TEXT
+               AND uw.window_minute >= to_char(NOW() - INTERVAL '1 minute', 'YYYY-MM-DDTHH24:MI')
              WHERE pk.provider_id = $1 AND pk.is_active = TRUE
                AND (pk.cooldown_until IS NULL OR pk.cooldown_until::timestamptz <= $2)
              GROUP BY pk.id, pk.key_value, pk.priority, pk.max_rpm, pk.max_tpm
@@ -200,7 +200,7 @@ pub async fn record_key_usage(
 
     // 3. 清理过期的滑动窗口行（保留最近 2 分钟即可）
     let _ = sqlx::query(
-        "DELETE FROM key_usage_window WHERE window_minute < (NOW() - INTERVAL '2 minutes')::TEXT"
+        "DELETE FROM key_usage_window WHERE window_minute < to_char(NOW() - INTERVAL '2 minutes', 'YYYY-MM-DDTHH24:MI')"
     )
     .execute(db).await; // 忽略错误，非关键操作
 

crates/zclaw-saas/src/relay/service.rs

@@ -651,7 +651,7 @@ pub async fn sort_candidates_by_quota(
                    SUM(COALESCE(pk.max_rpm, 999999) - COALESCE(uw.request_count, 0)) AS remaining_rpm
             FROM provider_keys pk
             LEFT JOIN key_usage_window uw ON pk.id = uw.key_id
-                AND uw.window_minute = to_char(date_trunc('minute', NOW()), 'YYYY-MM-DDTHH24:MI')
+                AND uw.window_minute >= to_char(NOW() - INTERVAL '1 minute', 'YYYY-MM-DDTHH24:MI')
             WHERE pk.provider_id = ANY($1)
               AND pk.is_active = TRUE
               AND (pk.cooldown_until IS NULL OR pk.cooldown_until::timestamptz <= NOW())