feat(test-catalog): add template creation and lead-approval workflow

Leads get a Create Template button that adds directly to the catalog
(existing POST /test-templates). Operators (red_tech/blue_tech) get the
same button, but their proposal now lands in a new template_suggestions
review queue instead — a lead on their team can approve it as-is, edit
fields before approving, or discard it. Modeled on the existing
ProcedureSuggestion review workflow.

backend/app/models/template_suggestion.py

@@ -0,0 +1,53 @@
+"""SQLAlchemy model for operator-proposed test templates, pending lead review.
+
+Leads create templates directly (see TestTemplateCreate router). An
+operator (red_tech/blue_tech) gets the same "create template" action, but
+their submission lands here instead of the live catalog — a lead on their
+team reviews it, optionally edits any field, and either approves it (which
+creates the real TestTemplate) or discards it.
+"""
+
+import uuid
+
+from sqlalchemy import Column, DateTime, ForeignKey, String, Text, func
+from sqlalchemy.dialects.postgresql import UUID
+from sqlalchemy.orm import relationship
+
+from app.database import Base
+
+
+class TemplateSuggestion(Base):
+    """A proposed new TestTemplate submitted by an operator, pending lead review."""
+
+    __tablename__ = "template_suggestions"
+
+    id = Column(UUID(as_uuid=True), primary_key=True, default=uuid.uuid4)
+
+    # Proposed TestTemplate fields — mirrors TestTemplateCreate.
+    mitre_technique_id = Column(String, nullable=False)
+    name = Column(String, nullable=False)
+    description = Column(Text, nullable=True)
+    source = Column(String, nullable=False, default="custom", server_default="custom")
+    source_url = Column(String, nullable=True)
+    attack_procedure = Column(Text, nullable=True)
+    expected_detection = Column(Text, nullable=True)
+    platform = Column(String, nullable=True)
+    tool_suggested = Column(String, nullable=True)
+    severity = Column(String, nullable=True)
+    atomic_test_id = Column(String, nullable=True)
+    suggested_remediation = Column(Text, nullable=True)
+
+    # "red" or "blue" — derived from the submitter's role, determines which
+    # lead reviews it (admins can review both).
+    team = Column(String(10), nullable=False)
+    submitted_by = Column(UUID(as_uuid=True), ForeignKey("users.id"), nullable=True)
+
+    status = Column(String(10), nullable=False, default="pending", server_default="pending")  # pending/approved/rejected
+    reviewed_by = Column(UUID(as_uuid=True), ForeignKey("users.id"), nullable=True)
+    reviewed_at = Column(DateTime, nullable=True)
+    created_template_id = Column(UUID(as_uuid=True), ForeignKey("test_templates.id"), nullable=True)
+    created_at = Column(DateTime(timezone=True), server_default=func.now())
+
+    submitter = relationship("User", foreign_keys=[submitted_by])
+    reviewer = relationship("User", foreign_keys=[reviewed_by])
+    created_template = relationship("TestTemplate", foreign_keys=[created_template_id])