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/models/procurement.py

@@ -66,6 +66,47 @@ class User(Base):
     created_at: Mapped[datetime] = _timestamptz()
 
 
+class UserPanel(Base):
+    """user_panels — تخصیص پنل + سطح دسترسی به کاربر (جایگزین مدل نقش).
+
+    panel:  'procurement' | 'inventory' | 'pm'
+    level:  'full'    — تدارکات: تغییر کامل در کل پنل؛ انبار: همه پروژه‌ها
+                        (به‌جز تغییر موجودی)
+            'limited' — تدارکات: فقط افزودن استعلام برای پروژه‌های عضویت؛
+                        انبار: فقط پروژه‌های عضویت + امکان تغییر موجودی
+    """
+
+    __tablename__ = "user_panels"
+
+    id: Mapped[uuid.UUID] = _uuid_pk()
+    user_id: Mapped[uuid.UUID] = mapped_column(
+        ForeignKey("users.id", ondelete="CASCADE"), nullable=False, index=True
+    )
+    panel: Mapped[str] = mapped_column(Text, nullable=False)
+    level: Mapped[str] = mapped_column(Text, nullable=False)
+    created_at: Mapped[datetime] = _timestamptz()
+
+    __table_args__ = (UniqueConstraint("user_id", "panel", name="uq_user_panel"),)
+
+
+class UserProjectMembership(Base):
+    """user_project_members — عضویت M:N کاربر در پروژه‌ها، جدا از مسئولیت
+    پروژه (projects.pm_user_id). محدوده‌ی داده‌ی سطح limited را تعیین می‌کند."""
+
+    __tablename__ = "user_project_members"
+
+    id: Mapped[uuid.UUID] = _uuid_pk()
+    user_id: Mapped[uuid.UUID] = mapped_column(
+        ForeignKey("users.id", ondelete="CASCADE"), nullable=False, index=True
+    )
+    project_id: Mapped[uuid.UUID] = mapped_column(
+        ForeignKey("projects.id", ondelete="CASCADE"), nullable=False, index=True
+    )
+    created_at: Mapped[datetime] = _timestamptz()
+
+    __table_args__ = (UniqueConstraint("user_id", "project_id", name="uq_user_project_member"),)
+
+
 class Supplier(Base):
     __tablename__ = "suppliers"