feat(governance): surface stale km priority queue

apps/api/src/models/governance.py

@@ -199,6 +199,48 @@ class KnowledgeReviewDraftArchiveResponse(BaseModel):
     generated_at: datetime
 
 
+# =============================================================================
+# Endpoint 2C: KM stale candidates
+# =============================================================================
+
+class KnowledgeStaleCandidate(BaseModel):
+    entry_id: str
+    project_id: str
+    title: str
+    entry_type: str
+    category: str | None = None
+    status: str
+    source: str | None = None
+    updated_at: datetime | None = None
+    stale_days: int
+    view_count: int
+    priority_score: int
+    priority_tier: Literal["P0", "P1", "P2"]
+    recommended_action: Literal[
+        "refresh_with_evidence",
+        "owner_review",
+        "archive_or_supersede",
+    ]
+    reasons: list[str] = Field(default_factory=list)
+    correlation_sources: list[str] = Field(default_factory=list)
+    related_incident_id: str | None = None
+    related_playbook_id: str | None = None
+    related_approval_id: str | None = None
+    tags: list[str] = Field(default_factory=list)
+
+
+class KnowledgeStaleCandidatesResponse(BaseModel):
+    schema_version: str = "km_stale_candidates_v1"
+    project_id: str
+    total_stale: int
+    returned: int
+    threshold_days: int
+    writes_on_read: bool = False
+    manual_review_required: bool = True
+    items: list[KnowledgeStaleCandidate]
+    generated_at: datetime
+
+
 # =============================================================================
 # Endpoint 3: summary
 # =============================================================================