Node page Discord picker: org's linked servers + voice channels, not raw IDs (#213 item 3, #109 item 13)

- c2-core routers/discord_web.py:
  PUT  /discord/guilds/{id}/directory (service key): the server bot pushes each
       server's name + voice channels; merged onto discord_guilds, never touches org_id.
  GET  /discord/nodes/{id}/join-options: the node org's servers (same
       resolve rule as the bot), their voice channels with any live stream,
       radio-bot readiness + invite links, and this node's streams. No tokens.
  POST /discord/nodes/{id}/streams: stream pinned to the node; server must be
       the node org's, channel must be in the bot's directory, guild + node caps.
  POST /discord/nodes/{id}/streams/stop: one stream on this node, or all.
  Control = platform admin, org owner, or operator owning the node.
- nodes.py: legacy raw-ID discord_join now refuses a server outside the node's org.
- discord bot: DirectorySync cog pushes on ready (15-min loop), join/leave,
  rename, voice/category channel changes (debounced).
- frontend: NodeDiscordRadio panel + picker replaces DiscordJoinModal and the
  admin-only Join/Leave buttons.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

drb-server-discord-bot/app/bot.py

@@ -13,6 +13,7 @@ class DRBBot(commands.Bot):
     async def setup_hook(self):
         await self.load_extension("app.commands.radio")
         await self.load_extension("app.commands.trips")
+        await self.load_extension("app.commands.directory")
 
         if settings.dev_guild_id:
             guild = discord.Object(id=settings.dev_guild_id)