Fix fcitx5 backend for system-wide installation.

The upstream code assumes a development layout where fcitx5/backend/ sits
alongside the app/ package. When installed system-wide:

- vocotype.cpp hardcodes ~/.local paths for the Python interpreter and
  audio_recorder.py script. Use system paths with user-install fallback.

- fcitx5_server.py and audio_recorder.py use sys.path hacks to import
  from the app package. Remove the hacks since distutils installs app/
  into site-packages. Change "from backend.rime_handler" to
  "from app.rime_handler" since rime_handler.py is copied into app/.

diff -urN a/fcitx5/addon/vocotype.cpp b/fcitx5/addon/vocotype.cpp
--- a/fcitx5/addon/vocotype.cpp
+++ b/fcitx5/addon/vocotype.cpp
@@ -66,8 +66,15 @@
     // 获取安装路径
     const char* home = std::getenv("HOME");
     if (home) {
-        python_venv_path_ = std::string(home) + "/.local/share/vocotype-fcitx5/.venv/bin/python";
-        recorder_script_path_ = std::string(home) + "/.local/share/vocotype-fcitx5/backend/audio_recorder.py";
+        // Try system-wide installation first
+        python_venv_path_ = "/usr/bin/python3";
+        recorder_script_path_ = "/usr/share/vocotype/audio_recorder.py";
+
+        // Fall back to user installation if system script not found
+        if (access(recorder_script_path_.c_str(), R_OK) != 0) {
+            python_venv_path_ = std::string(home) + "/.local/share/vocotype-fcitx5/.venv/bin/python";
+            recorder_script_path_ = std::string(home) + "/.local/share/vocotype-fcitx5/backend/audio_recorder.py";
+        }
     } else {
         FCITX_ERROR() << "HOME environment variable not set";
     }
diff -urN a/fcitx5/backend/audio_recorder.py b/fcitx5/backend/audio_recorder.py
--- a/fcitx5/backend/audio_recorder.py
+++ b/fcitx5/backend/audio_recorder.py
@@ -22,10 +22,6 @@
 import numpy as np
 import sounddevice as sd

-# 添加项目根目录到 path
-PROJECT_ROOT = Path(__file__).parent.parent.parent
-sys.path.insert(0, str(PROJECT_ROOT))
-
 from app.audio_utils import load_audio_config, resample_audio, SAMPLE_RATE
 from app.wave_writer import write_wav

diff -urN a/fcitx5/backend/fcitx5_server.py b/fcitx5/backend/fcitx5_server.py
--- a/fcitx5/backend/fcitx5_server.py
+++ b/fcitx5/backend/fcitx5_server.py
@@ -16,14 +16,10 @@
 import threading
 from pathlib import Path

-# 添加项目根目录到 path
-PROJECT_ROOT = Path(__file__).parent.parent
-sys.path.insert(0, str(PROJECT_ROOT))
-
 from app.config import DEFAULT_CONFIG, ensure_logging_dir, load_config
 from app.funasr_server import FunASRServer
 from app.logging_config import setup_logging
-from backend.rime_handler import RimeHandler
+from app.rime_handler import RimeHandler

 logger = logging.getLogger(__name__)