feat: add user display profiles and fix web context menu UX

backend:

- add required user name and optional bio fields

- extend auth/register and user schemas/services with name/bio

- add alembic migration 0006 with safe backfill name=username

- compute per-user chat display_title for private chats

- keep Saved Messages delete-for-all protections

web:

- registration now includes name

- add profile edit modal (name/username/bio/avatar url)

- show private chat names via display_title

- fix context menus to open near cursor with viewport clamping

- stabilize +/close floating button to remove visual jump

app/users/schemas.py

@@ -4,6 +4,7 @@ from pydantic import BaseModel, ConfigDict, EmailStr, Field
 
 
 class UserBase(BaseModel):
+    name: str = Field(min_length=1, max_length=100)
     username: str = Field(min_length=3, max_length=50)
     email: EmailStr
 
@@ -17,13 +18,16 @@ class UserRead(UserBase):
 
     id: int
     avatar_url: str | None = None
+    bio: str | None = None
     email_verified: bool
     created_at: datetime
     updated_at: datetime
 
 
 class UserProfileUpdate(BaseModel):
+    name: str | None = Field(default=None, min_length=1, max_length=100)
     username: str | None = Field(default=None, min_length=3, max_length=50)
+    bio: str | None = Field(default=None, max_length=500)
     avatar_url: str | None = Field(default=None, max_length=512)
 
 
@@ -31,5 +35,6 @@ class UserSearchRead(BaseModel):
     model_config = ConfigDict(from_attributes=True)
 
     id: int
+    name: str
     username: str
     avatar_url: str | None = None