Unify all timestamps to Beijing time (UTC+8)

- Add BEIJING_TZ constant in config.py
- Replace all timezone.utc references across 11 files
- Device-reported times, DB defaults, protocol sync all use Beijing time

via [HAPI](https://hapi.run)

Co-Authored-By: HAPI <noreply@hapi.run>

app/tcp_server.py

@@ -14,6 +14,8 @@ import asyncio
 import logging
 import struct
 from datetime import datetime, timezone
+
+from app.config import BEIJING_TZ
 from typing import Any, Dict, Optional, Tuple
 
 from sqlalchemy import select, update
@@ -240,7 +242,7 @@ class ConnectionInfo:
     def __init__(self, addr: Tuple[str, int]) -> None:
         self.imei: Optional[str] = None
         self.addr = addr
-        self.connected_at = datetime.now(timezone.utc)
+        self.connected_at = datetime.now(BEIJING_TZ)
         self.last_activity = self.connected_at
         self.serial_counter: int = 1
 
@@ -331,7 +333,7 @@ class TCPManager:
                     break
 
                 recv_buffer += data
-                conn_info.last_activity = datetime.now(timezone.utc)
+                conn_info.last_activity = datetime.now(BEIJING_TZ)
                 logger.info("Received %d bytes from %s:%d (IMEI=%s): %s",
                     len(data), addr[0], addr[1], conn_info.imei, data[:50].hex())
 
@@ -555,12 +557,12 @@ class TCPManager:
 
     @staticmethod
     def _parse_datetime(content: bytes, offset: int = 0) -> Optional[datetime]:
-        """Parse a 6-byte datetime field at *offset* and return a UTC datetime."""
+        """Parse a 6-byte datetime field at *offset* and return a Beijing-time datetime."""
         if len(content) < offset + 6:
             return None
         yy, mo, dd, hh, mi, ss = struct.unpack_from("BBBBBB", content, offset)
         try:
-            return datetime(2000 + yy, mo, dd, hh, mi, ss, tzinfo=timezone.utc)
+            return datetime(2000 + yy, mo, dd, hh, mi, ss, tzinfo=BEIJING_TZ)
         except ValueError:
             return None
 
@@ -634,7 +636,7 @@ class TCPManager:
             lang_str = "zh" if lang_code == 1 else "en" if lang_code == 2 else str(lang_code)
 
         # Persist device record
-        now = datetime.now(timezone.utc)
+        now = datetime.now(BEIJING_TZ)
         try:
             async with async_session() as session:
                 async with session.begin():
@@ -731,7 +733,7 @@ class TCPManager:
             if ext_info:
                 extension_data = ext_info
 
-        now = datetime.now(timezone.utc)
+        now = datetime.now(BEIJING_TZ)
 
         try:
             async with async_session() as session:
@@ -854,7 +856,7 @@ class TCPManager:
 
         content = pkt["content"]
         proto = pkt["protocol"]
-        now = datetime.now(timezone.utc)
+        now = datetime.now(BEIJING_TZ)
 
         # Parse recorded_at from the 6-byte datetime at offset 0
         recorded_at = self._parse_datetime(content, 0) or now
@@ -1247,7 +1249,7 @@ class TCPManager:
         if len(content) >= 8:
             language = struct.unpack("!H", content[6:8])[0]
 
-        now = datetime.now(timezone.utc)
+        now = datetime.now(BEIJING_TZ)
         if language == 0x0001:
             # Chinese: use GMT+8 timestamp
             ts = int(now.timestamp()) + 8 * 3600
@@ -1269,7 +1271,7 @@ class TCPManager:
         conn_info: ConnectionInfo,
     ) -> None:
         """Handle time sync 2 request (0x8A). Respond with YY MM DD HH MM SS."""
-        now = datetime.now(timezone.utc)
+        now = datetime.now(BEIJING_TZ)
         payload = bytes(
             [
                 now.year % 100,
@@ -1361,7 +1363,7 @@ class TCPManager:
 
         content = pkt["content"]
         proto = pkt["protocol"]
-        now = datetime.now(timezone.utc)
+        now = datetime.now(BEIJING_TZ)
 
         recorded_at = self._parse_datetime(content, 0) or now
 
@@ -1660,7 +1662,7 @@ class TCPManager:
         imei = conn_info.imei
         content = pkt["content"]
         proto = pkt["protocol"]
-        now = datetime.now(timezone.utc)
+        now = datetime.now(BEIJING_TZ)
 
         # -- Parse fields --
         pos = 0
@@ -1886,7 +1888,7 @@ class TCPManager:
         """
         content = pkt["content"]
         imei = conn_info.imei
-        now = datetime.now(timezone.utc)
+        now = datetime.now(BEIJING_TZ)
 
         # -- Parse 0xB2 fields --
         pos = 0
@@ -2036,7 +2038,7 @@ class TCPManager:
         """
         content = pkt["content"]
         imei = conn_info.imei
-        now = datetime.now(timezone.utc)
+        now = datetime.now(BEIJING_TZ)
 
         pos = 0
         recorded_at = self._parse_datetime(content, pos) or now
@@ -2293,7 +2295,7 @@ class TCPManager:
             except Exception:
                 response_text = content[5:].hex()
 
-        now = datetime.now(timezone.utc)
+        now = datetime.now(BEIJING_TZ)
 
         try:
             async with async_session() as session: