feat(knowledge-base): KnowledgeBase feature — models, CRUD API, RBAC

New entities mirroring the Project shape:
- knowledge_bases (human code, title, description, created_by, timestamps)
- knowledge_topics (UNIQUE(topic, knowledge_base_id))
- knowledge_categories (self-referential parent; UNIQUE(topic_id, parent, name),
  with an app-level check for the NULL-parent case MySQL can't enforce)
- knowledge_facts (category_id NULL → fact lives directly on the topic)
- project_knowledge_bases (M2M project ↔ knowledge base)

Adds full CRUD for KB/topic/category/fact, a nested /tree aggregate,
project link/unlink/list, KB-code generation (same algorithm as project
codes), and category cycle-prevention. Four global permissions
(knowledge-base.create/read/update/delete) seeded in init_bootstrap and
granted to admin/mgr/dev/general-agent/guest as appropriate. New tables
auto-create via Base.metadata.create_all; router wired in main.py.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

app/schemas/knowledge.py

@@ -0,0 +1,166 @@
+"""Pydantic schemas for the Knowledge Base feature."""
+from pydantic import BaseModel
+from typing import Optional, List
+from datetime import datetime
+
+
+# --------------------------------------------------------------------------
+# Knowledge Base
+# --------------------------------------------------------------------------
+class KnowledgeBaseBase(BaseModel):
+    title: str
+    description: Optional[str] = None
+
+
+class KnowledgeBaseCreate(KnowledgeBaseBase):
+    pass
+
+
+class KnowledgeBaseUpdate(BaseModel):
+    title: Optional[str] = None
+    description: Optional[str] = None
+
+
+class KnowledgeBaseResponse(BaseModel):
+    id: int
+    knowledge_base_code: Optional[str] = None
+    title: str
+    description: Optional[str] = None
+    created_by: int
+    created_at: Optional[datetime] = None
+    last_updated_at: Optional[datetime] = None
+
+    class Config:
+        from_attributes = True
+
+
+# --------------------------------------------------------------------------
+# Topic
+# --------------------------------------------------------------------------
+class KnowledgeTopicBase(BaseModel):
+    topic: str
+    description: Optional[str] = None
+
+
+class KnowledgeTopicCreate(KnowledgeTopicBase):
+    pass
+
+
+class KnowledgeTopicUpdate(BaseModel):
+    topic: Optional[str] = None
+    description: Optional[str] = None
+
+
+class KnowledgeTopicResponse(BaseModel):
+    id: int
+    topic: str
+    knowledge_base_id: int
+    description: Optional[str] = None
+    created_by: int
+    created_at: Optional[datetime] = None
+    last_updated_at: Optional[datetime] = None
+
+    class Config:
+        from_attributes = True
+
+
+# --------------------------------------------------------------------------
+# Category
+# --------------------------------------------------------------------------
+class KnowledgeCategoryBase(BaseModel):
+    name: str
+    description: Optional[str] = None
+
+
+class KnowledgeCategoryCreate(KnowledgeCategoryBase):
+    topic_id: int
+    parent: Optional[int] = None
+
+
+class KnowledgeCategoryUpdate(BaseModel):
+    name: Optional[str] = None
+    description: Optional[str] = None
+    parent: Optional[int] = None
+
+
+class KnowledgeCategoryResponse(BaseModel):
+    id: int
+    name: str
+    parent: Optional[int] = None
+    topic_id: int
+    description: Optional[str] = None
+    created_by: Optional[int] = None
+    last_updated_by: Optional[int] = None
+
+    class Config:
+        from_attributes = True
+
+
+# --------------------------------------------------------------------------
+# Fact
+# --------------------------------------------------------------------------
+class KnowledgeFactBase(BaseModel):
+    fact: str
+
+
+class KnowledgeFactCreate(KnowledgeFactBase):
+    topic_id: int
+    category_id: Optional[int] = None
+
+
+class KnowledgeFactUpdate(BaseModel):
+    fact: Optional[str] = None
+    category_id: Optional[int] = None
+
+
+class KnowledgeFactResponse(BaseModel):
+    id: int
+    category_id: Optional[int] = None
+    topic_id: int
+    fact: str
+    last_updated_at: Optional[datetime] = None
+
+    class Config:
+        from_attributes = True
+
+
+# --------------------------------------------------------------------------
+# Project <-> KnowledgeBase link
+# --------------------------------------------------------------------------
+class ProjectKnowledgeBaseLink(BaseModel):
+    # Accept either a numeric id or a knowledge_base_code (mirrors how
+    # projects are referenced elsewhere).
+    knowledge_base: str
+
+
+# --------------------------------------------------------------------------
+# Nested tree (read-only aggregate)
+# --------------------------------------------------------------------------
+class CategoryTreeNode(BaseModel):
+    id: int
+    name: str
+    parent: Optional[int] = None
+    topic_id: int
+    description: Optional[str] = None
+    categories: List["CategoryTreeNode"] = []
+    facts: List[KnowledgeFactResponse] = []
+
+
+class TopicTreeNode(BaseModel):
+    id: int
+    topic: str
+    knowledge_base_id: int
+    description: Optional[str] = None
+    categories: List[CategoryTreeNode] = []
+    facts: List[KnowledgeFactResponse] = []
+
+
+class KnowledgeBaseTree(BaseModel):
+    id: int
+    knowledge_base_code: Optional[str] = None
+    title: str
+    description: Optional[str] = None
+    topics: List[TopicTreeNode] = []
+
+
+CategoryTreeNode.model_rebuild()