feat(settings): add proxy support for model downloads and update checks (#909)

* feat(settings): add proxy support for model downloads and update checks

Add a Proxy page to Settings (above About) with Off / System / Manual
modes. Manual mode supports SOCKS5 and HTTPS (HTTP CONNECT) proxies
with optional username/password auth; the password is stored in
config.json in plaintext like the other settings. System mode honors
the *_proxy environment variables and falls back to the GNOME
org.gnome.system.proxy manual configuration.

The resolved proxy is applied to every in-app outbound path that
fetches models or checks updates: the shared requests download path in
recognition_manager (_stream_model_download, used by the whisper.cpp,
whisper, Vosk, Parakeet and faster-whisper downloaders) and the
release checks in update_checker. A small Test Connection button on
the Proxy page verifies reachability through the configured proxy.

SOCKS5 needs PySocks, added as a runtime dependency; uv.lock, the
requirements/*.txt exports and the Flatpak dependency manifest are
regenerated by just lock (with a fix in sync_flatpak_deps.py for
packages like PySocks that publish more than one universal wheel).

Fixes #655

* fix(proxy): bracket IPv6 hosts, escape test errors, declare pysocks for AUR

---------

Co-authored-by: Jatin K Malik <jatinkrmalik@gmail.com>

packaging/flatpak/python3-dependencies.yaml

@@ -113,6 +113,15 @@ modules:
       - *id004
       - *id005
       - *id006
+  - name: python3-pysocks
+    buildsystem: simple
+    build-commands:
+      - pip3 install --verbose --exists-action=i --no-index --find-links="file://${PWD}"
+        --prefix=${FLATPAK_DEST} "pysocks" --no-build-isolation
+    sources:
+      - type: file
+        url: https://files.pythonhosted.org/packages/8d/59/b4572118e098ac8e46e399a1dd0f2d85403ce8bbaad9ec79373ed6badaf9/PySocks-1.7.1-py3-none-any.whl
+        sha256: 2725bd0a9925919b9b51739eea5f9e2bae91e83288108a9ad338b2e3a4435ee5
   - name: python3-tqdm
     buildsystem: simple
     build-commands: