fix(identity): share one model-download user agent definition

Both model-download call sites built the User-Agent string separately:
recognition_manager used a hardcoded literal while settings_dialog
interpolated APP_ID. Add app_identity.user_agent() and use it in both,
with a test pinning the shared definition.

Fixes #17

src/vocalinux/app_identity.py

@@ -42,6 +42,12 @@ IBUS_TEXTDOMAIN: str = "voculinux"
 
 UPDATE_CHECKER_USER_AGENT: str = "Voculinux-UpdateChecker"
 
+
+def user_agent(version: str) -> str:
+    """Outbound HTTP User-Agent for model downloads."""
+    return f"{APP_ID}/{version}"
+
+
 RESOURCE_DIR_NAME: str = "voculinux"
 
 VERIFICATION_STAMP_NAME: str = ".voculinux_verified"

src/vocalinux/speech_recognition/recognition_manager.py

@@ -27,7 +27,7 @@ if TYPE_CHECKING:
     import numpy as np
     import requests
 
-from ..app_identity import APP_NAME, RESOURCE_DIR_NAME
+from ..app_identity import APP_NAME, RESOURCE_DIR_NAME, user_agent
 from ..audio.capture import (  # noqa: F401  (re-exported for compatibility)
     _STICKY_LOCK_MIN_MEAN_SQUARE,
     CaptureStalledError,
@@ -2731,7 +2731,7 @@ class SpeechRecognitionManager:
                     url,
                     stream=True,
                     timeout=self._MODEL_DOWNLOAD_TIMEOUT,
-                    headers={"User-Agent": f"voculinux/{__version__}"},
+                    headers={"User-Agent": user_agent(__version__)},
                     proxies=requests_proxies(),
                 )
             except requests.exceptions.RequestException as e:

src/vocalinux/ui/settings_dialog.py

@@ -36,7 +36,7 @@ gi.require_version("Gdk", "3.0")
 # Need GLib for idle_add
 from gi.repository import Gdk, GLib, GObject, Gtk, Pango  # noqa: E402
 
-from ..app_identity import APP_ID, APP_NAME, RESOURCE_DIR_NAME  # noqa: E402
+from ..app_identity import APP_NAME, RESOURCE_DIR_NAME, user_agent  # noqa: E402
 from ..audio.pulse_sources import (  # noqa: E402
     PULSE_INDEX_BASE,
     PulseSource,
@@ -6461,7 +6461,7 @@ class SettingsDialog(AboutSectionMixin):
             try:
                 response = requests.get(
                     "https://huggingface.co/api/models/ggerganov/whisper.cpp",
-                    headers={"User-Agent": f"{APP_ID}/{__version__}"},
+                    headers={"User-Agent": user_agent(__version__)},
                     timeout=10,
                     proxies=requests_proxies(config),
                 )