Refactor downloader and file manager for improved rclone integration and add healthcheck and smoke test options

- Renamed download flags in ContentDownloader for clarity.
- Enhanced FileManager with methods to build upload paths and verify existing files for rclone uploads.
- Updated StreamProcessor to return success status for stream processing.
- Added rclone smoke test and healthcheck functions to validate configuration and tool availability.
- Improved environment variable handling with a utility function.
- Updated TwitchArchive to incorporate new rclone verification and processing logic.
- Added unit tests for new functionality and refactored existing tests for clarity and coverage.

Co-authored-by: Copilot <copilot@github.com>

modules/utils.py

@@ -4,6 +4,7 @@ Utility functions and helpers for Twitch Archive.
 
 import os
 import sys
+import shutil
 import pathlib
 import subprocess
 from typing import Optional
@@ -35,6 +36,15 @@ def get_bin_path() -> str:
     return str(pathlib.Path(__file__).parent.parent.resolve() / "bin")
 
 
+def get_env_value(*names: str, default: Optional[str] = None) -> Optional[str]:
+    """Return the first non-empty environment variable from the provided names."""
+    for name in names:
+        value = os.getenv(name)
+        if value not in (None, ""):
+            return value
+    return default
+
+
 def get_ffmpeg_executable(os_type: str) -> str:
     """
     Get the platform-specific ffmpeg executable path.
@@ -48,6 +58,11 @@ def get_ffmpeg_executable(os_type: str) -> str:
     bin_path = get_bin_path()
     if os_type == 'windows':
         return os.path.join(bin_path, 'ffmpeg.exe')
+
+    system_ffmpeg = shutil.which('ffmpeg')
+    if system_ffmpeg:
+        return system_ffmpeg
+
     return os.path.join(bin_path, 'ffmpeg')
 
 
@@ -64,6 +79,11 @@ def get_twitch_downloader_executable(os_type: str) -> str:
     bin_path = get_bin_path()
     if os_type == 'windows':
         return os.path.join(bin_path, 'TwitchDownloaderCLI.exe')
+
+    system_twitch_downloader = shutil.which('TwitchDownloaderCLI')
+    if system_twitch_downloader:
+        return system_twitch_downloader
+
     return os.path.join(bin_path, 'TwitchDownloaderCLI')
 
 
@@ -164,6 +184,24 @@ def verify_streamlink() -> bool:
         return False
 
 
+def verify_rclone() -> bool:
+    """Verify that rclone is available on PATH."""
+    try:
+        result = subprocess.run(['rclone', 'version'],
+                              capture_output=True,
+                              text=True,
+                              timeout=5)
+        if result.returncode == 0:
+            version_line = result.stdout.strip().splitlines()[0] if result.stdout.strip() else 'unknown'
+            print(f'{Fore.GREEN}✓ Rclone found ({version_line}){Style.RESET_ALL}')
+            return True
+        raise FileNotFoundError()
+    except (FileNotFoundError, subprocess.TimeoutExpired, IndexError):
+        print(f'{Fore.RED}✗ ERROR: rclone not found{Style.RESET_ALL}')
+        print(f'{Fore.CYAN}  → Install rclone and ensure it is on PATH{Style.RESET_ALL}')
+        return False
+
+
 def verify_ffmpeg(os_type: str) -> bool:
     """
     Verify that ffmpeg is available.