Discord: channel list and presence without the main bot (server-26#225 S5)

A server linked to an org now shows in the node picker while a radio bot the
org may use is in it, even when the DRB server bot is absent or left. Its
voice-channel list is read from that radio bot's cached REST snapshot
(discord_rest.guild_directory, the same snapshot the permission check reads,
so no extra Discord request): inline when no list is stored, in the
background when the list is older than discord_directory_refresh_seconds.
The server bot's own fresh list still wins (back-compat) and its directory
push now drops the server's cached snapshots.

Guards: a server acting only through the unlinked-server fallback org still
needs the server bot; REST never creates a discord_guilds doc, never writes
org_id or bot_present, and never writes onto a server unlinked meanwhile.

Also fixes server-26#251: an interactive start (/join, admin page, web
picker, node discord_join) re-reads a cached "denied" snapshot older than
10 s once before refusing, so "fix it in Discord, then try again" works on
the next try. The reconciler never re-reads (no REST loop).

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

drb-c2-core/app/routers/nodes.py

@@ -210,7 +210,7 @@ async def send_command(
             doc = await discord_streams.start_stream(
                 org_id=node.get("org_id"), guild_id=cmd.guild_id, channel_id=cmd.channel_id,
                 system_id=system_id, node_id=node_id, preferred_token_id=cmd.preferred_token_id,
-                mode="adhoc",
+                mode="adhoc", interactive=True,
             )
         except discord_streams.StreamError as e:
             raise HTTPException(e.status, e.message)