Satisfy flake8 so the lint job stops failing

Pure formatting, no behaviour change: strip trailing whitespace from blank
lines, give top-level defs in system_cacher.py their two blank lines, wrap
the long discord_radio.join signature, and split the duplicated
active_config ternary in main.py and routers/api.py across lines.

Verified clean with flake8 --max-line-length=120, matching CI.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

drb-edge-node/app/internal/discord_radio.py

@@ -27,7 +27,8 @@ class RadioBot:
         self._channel_id: Optional[int] = None
         self._was_streaming: bool = False
 
-    async def join(self, guild_id: int, channel_id: int, token: str, call_active: bool = False, system_name: str = None) -> bool:
+    async def join(self, guild_id: int, channel_id: int, token: str,
+                   call_active: bool = False, system_name: str = None) -> bool:
         # (Re)start the bot if the token changed or the bot isn't running
         if self._current_token != token or not self._is_bot_running():
             if not await self._start_bot(token):