feat(user): implement user restrictions

## APIs Restricted for Restricted Users

A restricted user is blocked from performing the following actions, and will typically receive a `403 Forbidden` error:

*   **Chat & Notifications:**
    *   Sending any chat messages (public or private).
    *   Joining or leaving chat channels.
    *   Creating new PM channels.
*   **User Profile & Content:**
    *   Uploading a new avatar.
    *   Uploading a new profile cover image.
    *   Changing their username.
    *   Updating their userpage content.
*   **Scores & Gameplay:**
    *   Submitting scores in multiplayer rooms.
    *   Deleting their own scores (to prevent hiding evidence of cheating).
*   **Beatmaps:**
    *   Rating beatmaps.
    *   Taging beatmaps.
*   **Relationship:**
    *   Adding friends or blocking users.
    *   Removing friends or unblocking users.
*   **Teams:**
    *   Creating, updating, or deleting a team.
    *   Requesting to join a team.
    *   Handling join requests for a team they manage.
    *   Kicking a member from a team they manage.
*   **Multiplayer:**
    *   Creating or deleting multiplayer rooms.
    *   Joining or leaving multiplayer rooms.

## What is Invisible to Normal Users

*   **Leaderboards:**
    *   Beatmap leaderboards.
    *   Multiplayer (playlist) room leaderboards.
*   **User Search/Lists:**
    *   Restricted users will not appear in the results of the `/api/v2/users` endpoint.
    *   They will not appear in the list of a team's members.
*   **Relationship:**
    *   They will not appear in a user's friend list (`/friends`).
*   **Profile & History:**
    *   Attempting to view a restricted user's profile, events, kudosu history, or score history will result in a `404 Not Found` error, effectively making their profile invisible (unless the user viewing the profile is the restricted user themselves).
*   **Chat:**
    *   Normal users cannot start a new PM with a restricted user (they will get a `404 Not Found` error).
*   **Ranking:**
    *   Restricted users are excluded from any rankings.

### How to Restrict a User

Insert into `user_account_history` with `type=restriction`.

```sql
-- length is in seconds
INSERT INTO user_account_history (`description`, `length`, `permanent`, `timestamp`, `type`, `user_id`) VALUE ('some description', 86400, 0, '2025-10-05 01:00:00', 'RESTRICTION', 1);
```

---

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

app/router/v2/relationship.py

@@ -10,7 +10,7 @@ from .router import router
 
 from fastapi import HTTPException, Path, Query, Request, Security
 from pydantic import BaseModel
-from sqlmodel import exists, select
+from sqlmodel import col, exists, select
 
 
 @router.get(
@@ -63,6 +63,7 @@ async def get_relationship(
         select(Relationship).where(
             Relationship.user_id == current_user.id,
             Relationship.type == relationship_type,
+            ~User.is_restricted_query(col(Relationship.target_id)),
         )
     )
     if api_version >= 20241022 or relationship_type == RelationshipType.BLOCK:
@@ -110,7 +111,11 @@ async def add_relationship(
     target: Annotated[int, Query(description="目标用户 ID")],
     current_user: ClientUser,
 ):
-    if not (await db.exec(select(exists()).where(User.id == target))).first():
+    if await current_user.is_restricted(db):
+        raise HTTPException(403, "Your account is restricted and cannot perform this action.")
+    if not (
+        await db.exec(select(exists()).where((User.id == target) & ~User.is_restricted_query(col(User.id))))
+    ).first():
         raise HTTPException(404, "Target user not found")
 
     relationship_type = RelationshipType.FOLLOW if request.url.path.endswith("/friends") else RelationshipType.BLOCK
@@ -179,7 +184,11 @@ async def delete_relationship(
     target: Annotated[int, Path(..., description="目标用户 ID")],
     current_user: ClientUser,
 ):
-    if not (await db.exec(select(exists()).where(User.id == target))).first():
+    if await current_user.is_restricted(db):
+        raise HTTPException(403, "Your account is restricted and cannot perform this action.")
+    if not (
+        await db.exec(select(exists()).where((User.id == target) & ~User.is_restricted_query(col(User.id))))
+    ).first():
         raise HTTPException(404, "Target user not found")
 
     relationship_type = RelationshipType.BLOCK if "/blocks/" in request.url.path else RelationshipType.FOLLOW