Refactor web app for consistent style and improved error handling

Standardized string quoting to double quotes, improved formatting, and enhanced error handling throughout the Flask web app, i18n, and websocket handler modules. Updated test cases and main entry points for consistency. No functional changes, but code is now more readable and maintainable.

Author: dbccccccc

tests/test_web_app.py

@@ -37,16 +37,16 @@ def load_web_app(monkeypatch, **env):
 
 
 def test_voices_endpoint_returns_data(monkeypatch):
-    module = load_web_app(monkeypatch, REQUIRE_API_KEY='false', TTSFM_API_KEY=None)
+    module = load_web_app(monkeypatch, REQUIRE_API_KEY="false", TTSFM_API_KEY=None)
     client = module.app.test_client()
-    response = client.get('/api/voices')
+    response = client.get("/api/voices")
     assert response.status_code == 200
     payload = response.get_json()
-    assert payload['count'] == len(payload['voices'])
+    assert payload["count"] == len(payload["voices"])
 
 
 def test_combine_audio_chunks_uses_format_hint(monkeypatch):
-    load_web_app(monkeypatch, REQUIRE_API_KEY='false', TTSFM_API_KEY=None)
+    load_web_app(monkeypatch, REQUIRE_API_KEY="false", TTSFM_API_KEY=None)
 
     from ttsfm import audio as audio_module
 
@@ -82,17 +82,20 @@ def from_wav(cls, buffer):
     assert DummyAudioSegment.formats == ["wav", "wav"]
 
 
-@pytest.mark.parametrize('header_name, header_value', [
-    ('Authorization', 'Bearer super-secret'),
-    ('X-API-Key', 'super-secret'),
-])
+@pytest.mark.parametrize(
+    "header_name, header_value",
+    [
+        ("Authorization", "Bearer super-secret"),
+        ("X-API-Key", "super-secret"),
+    ],
+)
 def test_api_key_hash_verification(monkeypatch, header_name, header_value):
-    module = load_web_app(monkeypatch, REQUIRE_API_KEY='true', TTSFM_API_KEY='super-secret')
+    module = load_web_app(monkeypatch, REQUIRE_API_KEY="true", TTSFM_API_KEY="super-secret")
     client = module.app.test_client()
 
-    denied = client.post('/api/validate-text', json={'text': 'hello'})
+    denied = client.post("/api/validate-text", json={"text": "hello"})
     assert denied.status_code == 401
 
     headers = {header_name: header_value}
-    response = client.post('/api/validate-text', json={'text': 'hello'}, headers=headers)
+    response = client.post("/api/validate-text", json={"text": "hello"}, headers=headers)
     assert response.status_code == 200