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/main.py

@@ -79,6 +79,7 @@ from app.api.routers.schedule_type import router as schedule_type_router
 from app.api.routers.schedule_type_special_slot import router as schedule_type_special_slot_router
 from app.api.routers.calendar import router as calendar_router
 from app.api.routers.oidc import router as oidc_router
+from app.api.routers.knowledge import router as knowledge_router
 
 app.include_router(auth_router)
 app.include_router(oidc_router)
@@ -99,6 +100,7 @@ app.include_router(essentials_router)
 app.include_router(schedule_type_router)
 app.include_router(schedule_type_special_slot_router)
 app.include_router(calendar_router)
+app.include_router(knowledge_router)
 
 
 # Auto schema migration for lightweight deployments
@@ -488,7 +490,7 @@ def _sync_default_user_roles(db):
 @app.on_event("startup")
 def startup():
     from app.core.config import Base, engine, SessionLocal
-    from app.models import models, webhook, apikey, activity, milestone, notification, worklog, monitor, role_permission, task, support, meeting, proposal, propose, essential, agent, calendar, minimum_workload, schedule_type, schedule_type_special_slot, oidc_settings
+    from app.models import models, webhook, apikey, activity, milestone, notification, worklog, monitor, role_permission, task, support, meeting, proposal, propose, essential, agent, calendar, minimum_workload, schedule_type, schedule_type_special_slot, oidc_settings, knowledge
     Base.metadata.create_all(bind=engine)
     _migrate_schema()