feat(state-hub): add Extension Points and Technical Debt tracking

New entity types (DB tables, API routers, Pydantic schemas, Alembic
migration a3f1c2d4e5b6):
- extension_points: ep_id, domain, title, ep_type, status, priority,
  location, description, topic_id, workstream_id
- technical_debt: td_id, domain, title, debt_type, severity, status,
  location, description, topic_id, workstream_id

MCP server: 6 new tools — register_extension_point, list_extension_points,
update_ep_status, register_technical_debt, list_technical_debt,
update_td_status (each write emits a progress_event)

Dashboard: two new pages (extensions.md, techdept.md) with KPI sidebar,
charts, urgent-items section, and filterable card lists. Both added to
nav in observablehq.config.js.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

api/main.py

@@ -4,7 +4,7 @@ from fastapi import FastAPI
 from fastapi.middleware.cors import CORSMiddleware
 
 from api.database import engine
-from api.routers import decisions, progress, state, tasks, topics, workstreams, workstream_dependencies
+from api.routers import decisions, extension_points, progress, state, tasks, technical_debt, topics, workstreams, workstream_dependencies
 
 
 @asynccontextmanager
@@ -32,6 +32,8 @@ app.include_router(workstreams.router)
 app.include_router(workstream_dependencies.router)
 app.include_router(tasks.router)
 app.include_router(decisions.router)
+app.include_router(extension_points.router)
+app.include_router(technical_debt.router)
 app.include_router(progress.router)
 app.include_router(state.router)