RSS bot: populate channel on first run so joiners see content

Previously the bot seeded all existing feed items on startup WITHOUT posting, so a
freshly-created channel stayed empty and new subscribers saw nothing (only items
appearing after start were posted). Now on first run it posts the latest items
(max 5) to fill the channel — recent history then shows them to joiners — and sets
an rss_populated flag so restarts don't replay. Existing (empty) bots get filled
once on next start. Update rss_test.py.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

manager/rss_test.py

@@ -100,11 +100,12 @@ async def main() -> int:
         print("channel created:", bool(gid), "gid", gid)
         assert gid, "rss bot did not create a channel"
 
-        # 2) the first item was seeded, not posted
-        await asyncio.sleep(2)
-        texts = await channel_texts(b.chat, gid)
-        assert not any("First post" in t for t in texts), "seeded item was wrongly broadcast"
-        print("seed OK (first item not broadcast)")
+        # 2) first run populates the channel with the existing item(s)
+        got_initial = await wait_until(
+            lambda: _contains(channel_texts(b.chat, gid), "First post"), timeout=20, every=2
+        )
+        print("initial item populated to channel:", bool(got_initial))
+        assert got_initial, "channel was not populated on first run"
 
         # 3) add a new item → it should be broadcast on the next poll
         FEED["items"].insert(0, ("Breaking news", "https://example.com/2"))