feat: add reply/forward/pin message flow across backend and web

- add reply_to/forwarded_from message fields and chat pinned_message field

- add forward and pin APIs plus reply support in message create

- wire web actions: Reply, Fwd, Pin and reply composer state

- fix spam policy bug: allow repeated identical messages, keep rate limiting

app/messages/schemas.py

@@ -12,6 +12,8 @@ class MessageRead(BaseModel):
     id: int
     chat_id: int
     sender_id: int
+    reply_to_message_id: int | None
+    forwarded_from_message_id: int | None
     type: MessageType
     text: str | None
     created_at: datetime
@@ -23,6 +25,7 @@ class MessageCreateRequest(BaseModel):
     type: MessageType = MessageType.TEXT
     text: str | None = Field(default=None, max_length=4096)
     client_message_id: str | None = Field(default=None, min_length=8, max_length=64)
+    reply_to_message_id: int | None = None
 
 
 class MessageUpdateRequest(BaseModel):
@@ -33,3 +36,7 @@ class MessageStatusUpdateRequest(BaseModel):
     chat_id: int
     message_id: int
     status: Literal["message_delivered", "message_read"]
+
+
+class MessageForwardRequest(BaseModel):
+    target_chat_id: int