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/app/routers/debug.py

@@ -9,9 +9,11 @@ router = APIRouter(prefix="/api/debug", tags=["debug"])
 def recent_requests():
     """Most-recent-first log of provider requests/responses (no API keys).
 
-    The log is a single process-wide ring buffer with no per-user
-    attribution, so in multi-user (hosted) mode it would leak other players'
-    prompts — disabled there, available on local installs."""
+    The log is a single process-wide ring buffer with no per-user attribution,
+    so in multi-user mode, which is how a hosted deployment runs, it would expose
+    other players' prompts. It is disabled there and available on a local
+    install.
+    """
     if auth.MULTI_USER:
         raise HTTPException(403, "The debug log is only available on local installs.")
     return debuglog.recent()