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/schemas/__init__.py

@@ -4,6 +4,8 @@ from api.schemas.task import TaskCreate, TaskUpdate, TaskRead
 from api.schemas.decision import DecisionCreate, DecisionUpdate, DecisionRead
 from api.schemas.progress_event import ProgressEventCreate, ProgressEventRead
 from api.schemas.state import StateSummary, Totals, TopicTotals, WorkstreamTotals, TaskTotals, DecisionTotals
+from api.schemas.extension_point import EPCreate, EPUpdate, EPRead
+from api.schemas.technical_debt import TDCreate, TDUpdate, TDRead
 
 __all__ = [
     "TopicCreate", "TopicUpdate", "TopicRead", "TopicWithWorkstreams",
@@ -12,4 +14,6 @@ __all__ = [
     "DecisionCreate", "DecisionUpdate", "DecisionRead",
     "ProgressEventCreate", "ProgressEventRead",
     "StateSummary", "Totals", "TopicTotals", "WorkstreamTotals", "TaskTotals", "DecisionTotals",
+    "EPCreate", "EPUpdate", "EPRead",
+    "TDCreate", "TDUpdate", "TDRead",
 ]