Matrix intake: main-timeline nudge, clearer messages, note text in grid

Four bot-side UX fixes surfaced by the live smoke:
- Post a brief pointer in the main timeline (a reply to the user's message)
  alongside the in-thread proposal card, so proposals aren't missed inside a
  thread. Pointer only — approvals still happen in the thread, where the note
  is visible (you can't make an informed yes/no without seeing it).
- A bare yes/no typed in the main timeline while a proposal is pending now
  gets a "reply in the thread" redirect instead of "couldn't tell what to record."
- Clearer commit confirmations: "Created a new grid entry for X" vs
  "Logged a note on X (existing grid entry)."
- Send a blank communication subject when a note is present so the grid's
  one-line note summary shows the note text, not the "(Matrix)" label
  (provenance stays in source="matrix_intake").

backend/matrix_intake/matrix_io.py

@@ -53,3 +53,21 @@ def make_say(client):
         for chunk in split_message(text):
             await client.room_send(room_id, "m.room.message", thread_content(chunk, thread_root))
     return say
+
+
+def reply_content(text, reply_to_event_id):
+    """Build a plain (non-threaded) reply: shows in the MAIN timeline as a reply to
+    reply_to_event_id, unlike thread_content() which lands the message inside a thread."""
+    content = {"msgtype": "m.text", "body": text}
+    if reply_to_event_id:
+        content["m.relates_to"] = {"m.in_reply_to": {"event_id": reply_to_event_id}}
+    return content
+
+
+def make_reply(client):
+    """Return an async reply(room_id, text, reply_to) that posts a plain main-timeline reply —
+    the brief 'proposed X — see thread' nudge alongside the in-thread proposal card."""
+    async def reply(room_id, text, reply_to):
+        for chunk in split_message(text):
+            await client.room_send(room_id, "m.room.message", reply_content(chunk, reply_to))
+    return reply