Ideas: add 'awaiting feedback' status with amber section + admin comment

Status cycles open → awaiting → done → reopen.
Awaiting ideas float to the top in a 'Waiting for your feedback' section
with an amber border (#f59e0b).

Admin can attach an implementation note to any awaiting idea via
POST /api/ideas/{id}/comment. The note appears inside the same card
in a distinct sub-box with a subtle amber tint border, editable inline.
The sub-box is visible to all users once a note exists.

bincio/serve/models.py

@@ -86,3 +86,7 @@ class CreateInviteRequest(BaseModel):
 class IdeaBody(BaseModel):
     title: str
     body: str = ""
+
+
+class IdeaCommentBody(BaseModel):
+    comment: str = ""