feat: 测活覆盖全部代理（含死记录），拨活即复活

ListProxiesDue 去掉 alive=1 限制：死代理每小时也重测，协议级握手
成功就 MarkProxyAlive 复活（fail_count 清零），不再只能等同步时
重新出现在源列表才复活。

附带：提取页加「带协议前缀」开关，复制链接自动带 fmt=url。

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Co-Authored-By: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

backend/internal/db/queries.sql

@@ -208,7 +208,7 @@ WHERE id = ?;
 DELETE FROM proxies WHERE id = ?;
 
 -- name: ListProxiesDue :many
-SELECT id, ip, port, protocols, fail_count FROM proxies WHERE alive = 1 AND last_checked_at < ? ORDER BY last_checked_at LIMIT 20000;
+SELECT id, ip, port, protocols, fail_count FROM proxies WHERE last_checked_at < ? ORDER BY last_checked_at LIMIT 20000;
 
 -- name: MarkProxyAlive :exec
 UPDATE proxies SET last_checked_at = ?, alive = 1, fail_count = 0, last_alive_at = ?, latency = ? WHERE id = ?;