feat(org): panel-based access system replacing roles (procurement/inventory)

- new tables user_panels (panel: procurement/inventory/pm + level full/limited)
  and user_project_members (M:N membership, separate from pm responsibility)
- UserContext carries panels + member_project_ids; /users/me and the users
  list include them
- admin endpoints: PUT /users/{id}/panels, PUT /users/{id}/panel-projects
- inventory scope: panel inventory 'full' -> manager scope (all projects, NO
  stock change); 'limited' -> supervisor scope (own memberships, stock change
  allowed); legacy roles kept as migration fallback; admin untouched
- procurement writes: _procurement_writer is now panel-aware (admin, legacy
  procurement_manager, or procurement 'full') across all 18 write routers;
  quote CREATE additionally allows 'limited' users restricted to their member
  projects (validated server-side)
- frontend: panel-aware HomeRoute (inventory -> warehouse panel, procurement
  limited -> minimal RequesterHome), wizard project options restricted for
  limited users, change-inventory button/route gated to inventory 'limited',
  organization panel gains the panels & access-levels management section

backend/app/schemas/procurement.py

@@ -346,3 +346,16 @@ class ReceiptUpdate(APIModel):
     received_qty: Decimal | None = Field(default=None, gt=0)
     on_time: bool | None = None
     quality_note: str | None = None
+
+
+class UserPanelsUpdate(APIModel):
+    """Replace the user's panel assignments. هر پنل: 'full' | 'limited' —
+    پنل غایب یعنی تخصیص نداشتن و کلید آن حذف می‌شود."""
+
+    panels: dict[str, str] = Field(default_factory=dict)
+
+
+class UserPanelProjectsUpdate(APIModel):
+    """Replace the user's project memberships (M:N — جدا از مسئولیت پروژه)."""
+
+    project_ids: list[UUID] = Field(default_factory=list)