Rewrite Python comments in Google developer documentation style (#12)

* Rewrite comments in Google developer documentation style

Rewrite the comments and docstrings across the backend core modules so they
read plainly. The previous prose was accurate but dense and figurative, which
made it slow to skim.

Applies the Google developer documentation style guide: short sentences, active
voice, present tense, American spelling, and no metaphors, idioms, or
rhetorical asides. Replaces em-dash chains with separate sentences.

backend/tests/test_netguard.py

@@ -22,7 +22,7 @@ def hosted(monkeypatch):
 
 
 def _resolves_to(monkeypatch, ip: str):
-    """Pin getaddrinfo so we test the address decision, not real DNS."""
+    """Pin `getaddrinfo` so the test exercises the address decision, not real DNS."""
     monkeypatch.setattr(
         netguard.socket, "getaddrinfo",
         lambda *a, **k: [(2, 1, 6, "", (ip, 443))],
@@ -64,6 +64,6 @@ def test_unresolvable_host_is_blocked(hosted, monkeypatch):
 
 def test_noop_in_local_mode(monkeypatch):
     monkeypatch.setattr(auth, "MULTI_USER", False)
-    # Local installs legitimately reach localhost (Ollama) — never blocked.
+    # Local installs must reach localhost (Ollama). The guard never blocks local mode.
     assert netguard.endpoint_block_reason("http://localhost:11434/v1") is None
     assert netguard.endpoint_block_reason("http://127.0.0.1:11434/v1") is None