feat: 文件快传新增共享剪贴板（跨客户端粘贴、查看与一键复制）

- 后端：新增 /api/clips（列表/新建）、/api/clips/<id>（取全文/删除）、/api/clips/<id>/copy（复制计数），列表仅返回 240 字符预览
- 存储：SQLite 新增 clips 表（含 expires_at 索引），启动自动建表，线上老库无需手工迁移
- 前端：剪贴板卡片支持读取本机剪贴板、来源备注、查看全文、一键复制到本机剪贴板、单条删除与复制次数
- 清理：systemd 定时任务与 /api/cleanup 同时清理过期剪贴板
- 配置：新增 max_clip_length / max_clips / clip_default_expires_hours
- 部署：deploy_transfer.py 新增 --keep-credentials（不重置登录密码与会话密钥）与 SSH 连接重试
- 文档：README / setup.md / CHANGELOG 同步更新

transfer/storage.py

@@ -16,8 +16,21 @@ CREATE TABLE IF NOT EXISTS files (
     expires_at  INTEGER NOT NULL,
     downloads   INTEGER NOT NULL DEFAULT 0
 );
+
+CREATE TABLE IF NOT EXISTS clips (
+    id          TEXT PRIMARY KEY,
+    content     TEXT NOT NULL,
+    client      TEXT NOT NULL DEFAULT '',
+    created_at  INTEGER NOT NULL,
+    expires_at  INTEGER NOT NULL,
+    copies      INTEGER NOT NULL DEFAULT 0
+);
+
+CREATE INDEX IF NOT EXISTS idx_clips_expires_at ON clips (expires_at);
 """
 
+CLIP_PREVIEW_CHARS = 240
+
 
 def connect(db_path: str) -> sqlite3.Connection:
     conn = sqlite3.connect(db_path, timeout=30)
@@ -172,3 +185,136 @@ def cleanup_orphans(db_path: str, files_dir: str, now: int | None = None,
         except OSError:
             pass
     return removed
+
+
+# ---------- 剪贴板（纯数据库存储，无磁盘文件） ----------
+
+def clip_to_dict(row: sqlite3.Row, now: int) -> dict:
+    """把带 preview/size 字段的查询行转换为接口返回结构（不含完整正文）。"""
+    size = row["size"] if row["size"] is not None else 0
+    return {
+        "id": row["id"],
+        "preview": row["preview"] or "",
+        "size": size,
+        "truncated": size > len(row["preview"] or ""),
+        "client": row["client"] or "",
+        "created_at": iso(row["created_at"]),
+        "expires_at": iso(row["expires_at"]),
+        "remaining_seconds": max(0, row["expires_at"] - now),
+        "copies": row["copies"],
+    }
+
+
+def insert_clip(db_path: str, clip_id: str, content: str, client: str,
+                expires_at: int, created_at: int) -> None:
+    with _DB_LOCK:
+        conn = connect(db_path)
+        try:
+            conn.execute(
+                "INSERT INTO clips (id, content, client, created_at, expires_at, copies) "
+                "VALUES (?, ?, ?, ?, ?, 0)",
+                (clip_id, content, client, created_at, expires_at),
+            )
+            conn.commit()
+        finally:
+            conn.close()
+
+
+def get_clip(db_path: str, clip_id: str, preview_chars: int = CLIP_PREVIEW_CHARS):
+    """返回单条剪贴板记录的完整内容（含 content 字段）。"""
+    with _DB_LOCK:
+        conn = connect(db_path)
+        try:
+            return conn.execute(
+                "SELECT id, content, client, created_at, expires_at, copies, "
+                "length(content) AS size FROM clips WHERE id = ?",
+                (clip_id,),
+            ).fetchone()
+        finally:
+            conn.close()
+
+
+def clip_content_to_dict(row: sqlite3.Row, now: int) -> dict:
+    return {
+        "id": row["id"],
+        "content": row["content"] or "",
+        "size": row["size"] if row["size"] is not None else 0,
+        "client": row["client"] or "",
+        "created_at": iso(row["created_at"]),
+        "expires_at": iso(row["expires_at"]),
+        "remaining_seconds": max(0, row["expires_at"] - now),
+        "copies": row["copies"],
+    }
+
+
+def list_clips(db_path: str, now: int,
+               preview_chars: int = CLIP_PREVIEW_CHARS) -> list[dict]:
+    """列出未过期剪贴板记录；只取正文前若干字符作为预览，避免列表响应过大。"""
+    with _DB_LOCK:
+        conn = connect(db_path)
+        try:
+            rows = conn.execute(
+                "SELECT id, client, created_at, expires_at, copies, "
+                "substr(content, 1, ?) AS preview, length(content) AS size "
+                "FROM clips WHERE expires_at > ? "
+                "ORDER BY created_at DESC, rowid DESC",
+                (preview_chars, now),
+            ).fetchall()
+            return [clip_to_dict(r, now) for r in rows]
+        finally:
+            conn.close()
+
+
+def increment_clip_copies(db_path: str, clip_id: str) -> bool:
+    with _DB_LOCK:
+        conn = connect(db_path)
+        try:
+            cur = conn.execute(
+                "UPDATE clips SET copies = copies + 1 WHERE id = ?", (clip_id,)
+            )
+            conn.commit()
+            return cur.rowcount > 0
+        finally:
+            conn.close()
+
+
+def delete_clip(db_path: str, clip_id: str) -> bool:
+    with _DB_LOCK:
+        conn = connect(db_path)
+        try:
+            cur = conn.execute("DELETE FROM clips WHERE id = ?", (clip_id,))
+            conn.commit()
+            return cur.rowcount > 0
+        finally:
+            conn.close()
+
+
+def cleanup_expired_clips(db_path: str, now: int | None = None) -> int:
+    import time as _time
+    now = now if now is not None else int(_time.time())
+    with _DB_LOCK:
+        conn = connect(db_path)
+        try:
+            cur = conn.execute("DELETE FROM clips WHERE expires_at <= ?", (now,))
+            conn.commit()
+            return cur.rowcount
+        finally:
+            conn.close()
+
+
+def prune_clips(db_path: str, keep: int) -> int:
+    """只保留最近 keep 条剪贴板记录，返回被删除的条数。"""
+    if keep <= 0:
+        return 0
+    with _DB_LOCK:
+        conn = connect(db_path)
+        try:
+            cur = conn.execute(
+                "DELETE FROM clips WHERE id NOT IN ("
+                "SELECT id FROM clips ORDER BY created_at DESC, rowid DESC LIMIT ?)",
+                (keep,),
+            )
+            conn.commit()
+            return cur.rowcount
+        finally:
+            conn.close()