feat: add Linux support with cross-platform memory scanning

- Add Linux memory scanner (`find_all_keys_linux.py`) using `/proc/<pid>/mem`,
  same approach as Windows/macOS — no GDB, no function offsets, no restart needed
- Extract Windows-specific code to `find_all_keys_windows.py`
- Make `find_all_keys.py` a platform dispatcher (Windows / Linux)
- Add `key_utils.py` for cross-platform path matching (`/` vs `\` in all_keys.json)
- Update `config.py` with Linux auto-detection of db_storage paths
- Update all consumers (decrypt_db, monitor, monitor_web, mcp_server) to use
  `get_key_info()` for platform-agnostic key lookup

Tested on remote Linux container: 15/15 DBs scanned, decrypted, and verified.

monitor.py

@@ -7,8 +7,9 @@ session.db 包含每个聊天的最新消息摘要、发送者、时间戳
 import hashlib, struct, os, sys, json, time, sqlite3, io
 import hmac as hmac_mod
 from datetime import datetime
-from Crypto.Cipher import AES
-import zstandard as zstd
+from Crypto.Cipher import AES
+import zstandard as zstd
+from key_utils import get_key_info, strip_key_metadata
 
 _zstd_dctx = zstd.ZstdDecompressor()
 
@@ -148,13 +149,13 @@ def main():
     print("=" * 60)
 
     # 加载密钥
-    with open(KEYS_FILE) as f:
-        keys = json.load(f)
-
-    session_key_info = keys.get("session/session.db")
-    if not session_key_info:
-        print("[ERROR] 找不到session.db的密钥")
-        sys.exit(1)
+    with open(KEYS_FILE) as f:
+        keys = strip_key_metadata(json.load(f))
+
+    session_key_info = get_key_info(keys, os.path.join("session", "session.db"))
+    if not session_key_info:
+        print("[ERROR] 找不到session.db的密钥")
+        sys.exit(1)
 
     enc_key = bytes.fromhex(session_key_info["enc_key"])
     session_db = os.path.join(DB_DIR, "session", "session.db")