chore(backend): repair test suite and bring ruff to green

The suite hadn't run green since the routes refactor:
- test_profile_duplicate_names.py imported the pre-refactor module
  layout and broke collection; now imports backend.services.profiles
- tests/conftest.py puts the repo root and backend dir on sys.path so
  files collect standalone instead of depending on run order
- test_cors.py tested a hand-copied mirror of the origin list that had
  drifted from app.py (missing http://tauri.localhost); it now builds
  the app via the real create_app() factory
- test_progress.py simulated a 1KB download, below the tracker's 1MB
  reporting threshold; simulation raised to 5MB
- slow/timeout markers registered in pyproject

Ruff: ~900 violations auto-fixed (typing modernization, import
sorting, unused imports, whitespace). The remaining rules are baselined
in pyproject.toml with per-rule counts to burn down, plus per-file
carve-outs for deliberate env-before-import ordering. ruff check is
now clean; suite is 134 passed, 2 skipped.

backend/utils/audio.py

@@ -2,10 +2,10 @@
 Audio processing utilities.
 """
 
+
+import librosa
 import numpy as np
 import soundfile as sf
-import librosa
-from typing import Tuple, Optional
 
 
 def normalize_audio(
@@ -15,32 +15,32 @@ def normalize_audio(
 ) -> np.ndarray:
     """
     Normalize audio to target loudness with peak limiting.
-    
+
     Args:
         audio: Input audio array
         target_db: Target RMS level in dB
         peak_limit: Peak limit (0.0-1.0)
-        
+
     Returns:
         Normalized audio array
     """
     # Convert to float32
     audio = audio.astype(np.float32)
-    
+
     # Calculate current RMS
     rms = np.sqrt(np.mean(audio**2))
-    
+
     # Calculate target RMS
     target_rms = 10**(target_db / 20)
-    
+
     # Apply gain
     if rms > 0:
         gain = target_rms / rms
         audio = audio * gain
-    
+
     # Peak limiting
     audio = np.clip(audio, -peak_limit, peak_limit)
-    
+
     return audio
 
 
@@ -48,15 +48,15 @@ def load_audio(
     path: str,
     sample_rate: int = 24000,
     mono: bool = True,
-) -> Tuple[np.ndarray, int]:
+) -> tuple[np.ndarray, int]:
     """
     Load audio file with normalization.
-    
+
     Args:
         path: Path to audio file
         sample_rate: Target sample rate
         mono: Convert to mono
-        
+
     Returns:
         Tuple of (audio_array, sample_rate)
     """
@@ -84,8 +84,8 @@ def save_audio(
     Raises:
         OSError: If file cannot be written
     """
-    from pathlib import Path
     import os
+    from pathlib import Path
 
     temp_path = f"{path}.tmp"
     try:
@@ -264,7 +264,7 @@ def validate_reference_audio(
     min_duration: float = 2.0,
     max_duration: float = 30.0,
     min_rms: float = 0.01,
-) -> Tuple[bool, Optional[str]]:
+) -> tuple[bool, str | None]:
     """
     Validate reference audio for voice cloning.
 
@@ -288,7 +288,7 @@ def validate_and_load_reference_audio(
     min_duration: float = 2.0,
     max_duration: float = 30.0,
     min_rms: float = 0.01,
-) -> Tuple[bool, Optional[str], Optional[np.ndarray], Optional[int]]:
+) -> tuple[bool, str | None, np.ndarray | None, int | None]:
     """
     Validate and load reference audio in a single pass.
 
@@ -315,4 +315,4 @@ def validate_and_load_reference_audio(
 
         return True, None, audio, sr
     except Exception as e:
-        return False, f"Error validating audio: {str(e)}", None, None
+        return False, f"Error validating audio: {e!s}", None, None