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/spam_guard.py

@@ -1,16 +1,9 @@
-import hashlib
-
 from fastapi import HTTPException, status
 from redis.exceptions import RedisError
 
 from app.config.settings import settings
 from app.utils.redis_client import get_redis_client
 
-
-def _hash_text(text: str) -> str:
-    return hashlib.sha256(text.encode("utf-8")).hexdigest()
-
-
 async def enforce_message_spam_policy(*, user_id: int, chat_id: int, text: str | None) -> None:
     redis = get_redis_client()
     rate_key = f"spam:msg_rate:{user_id}:{chat_id}"
@@ -23,15 +16,5 @@ async def enforce_message_spam_policy(*, user_id: int, chat_id: int, text: str |
                 status_code=status.HTTP_429_TOO_MANY_REQUESTS,
                 detail="Message rate limit exceeded for this chat.",
             )
-
-        normalized = (text or "").strip()
-        if normalized:
-            dup_key = f"spam:dup:{user_id}:{chat_id}:{_hash_text(normalized)}"
-            if await redis.exists(dup_key):
-                raise HTTPException(
-                    status_code=status.HTTP_429_TOO_MANY_REQUESTS,
-                    detail="Duplicate message cooldown is active.",
-                )
-            await redis.set(dup_key, "1", ex=settings.duplicate_message_cooldown_seconds)
     except RedisError:
         return