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/models/__init__.py

@@ -5,6 +5,8 @@ from api.models.workstream_dependency import WorkstreamDependency
 from api.models.task import Task, TaskStatus, TaskPriority
 from api.models.decision import Decision, DecisionType, DecisionStatus
 from api.models.progress_event import ProgressEvent
+from api.models.extension_point import ExtensionPoint, EPStatus
+from api.models.technical_debt import TechnicalDebt, TDStatus
 
 __all__ = [
     "Base",
@@ -14,4 +16,6 @@ __all__ = [
     "Task", "TaskStatus", "TaskPriority",
     "Decision", "DecisionType", "DecisionStatus",
     "ProgressEvent",
+    "ExtensionPoint", "EPStatus",
+    "TechnicalDebt", "TDStatus",
 ]

api/models/extension_point.py

@@ -0,0 +1,47 @@
+import enum
+import uuid
+
+from sqlalchemy import Enum, ForeignKey, String, Text
+from sqlalchemy.dialects.postgresql import UUID
+from sqlalchemy.orm import Mapped, mapped_column, relationship
+
+from api.models.base import Base, TimestampMixin, new_uuid
+
+
+class EPStatus(str, enum.Enum):
+    open = "open"
+    in_progress = "in_progress"
+    addressed = "addressed"
+    deferred = "deferred"
+    wont_fix = "wont_fix"
+
+
+class ExtensionPoint(Base, TimestampMixin):
+    __tablename__ = "extension_points"
+
+    id: Mapped[uuid.UUID] = mapped_column(
+        UUID(as_uuid=True), primary_key=True, default=new_uuid
+    )
+    ep_id: Mapped[str | None] = mapped_column(
+        String(30), nullable=True, unique=True, index=True
+    )  # human-readable ref, e.g. EP-CUST-001
+    domain: Mapped[str] = mapped_column(String(50), nullable=False, index=True)
+    title: Mapped[str] = mapped_column(String(255), nullable=False)
+    description: Mapped[str | None] = mapped_column(Text, nullable=True)
+    location: Mapped[str | None] = mapped_column(String(500), nullable=True)
+    ep_type: Mapped[str] = mapped_column(
+        String(50), nullable=False, default="other"
+    )  # api | schema | mcp | dashboard | architecture | integration | other
+    status: Mapped[EPStatus] = mapped_column(
+        Enum(EPStatus, name="epstatus"), nullable=False, default=EPStatus.open
+    )
+    priority: Mapped[str] = mapped_column(String(20), nullable=False, default="medium")
+    topic_id: Mapped[uuid.UUID | None] = mapped_column(
+        UUID(as_uuid=True), ForeignKey("topics.id", ondelete="SET NULL"), nullable=True
+    )
+    workstream_id: Mapped[uuid.UUID | None] = mapped_column(
+        UUID(as_uuid=True), ForeignKey("workstreams.id", ondelete="SET NULL"), nullable=True
+    )
+
+    topic: Mapped["Topic"] = relationship("Topic", lazy="selectin")  # noqa: F821
+    workstream: Mapped["Workstream"] = relationship("Workstream", lazy="selectin")  # noqa: F821

api/models/technical_debt.py

@@ -0,0 +1,47 @@
+import enum
+import uuid
+
+from sqlalchemy import Enum, ForeignKey, String, Text
+from sqlalchemy.dialects.postgresql import UUID
+from sqlalchemy.orm import Mapped, mapped_column, relationship
+
+from api.models.base import Base, TimestampMixin, new_uuid
+
+
+class TDStatus(str, enum.Enum):
+    open = "open"
+    in_progress = "in_progress"
+    resolved = "resolved"
+    deferred = "deferred"
+    wont_fix = "wont_fix"
+
+
+class TechnicalDebt(Base, TimestampMixin):
+    __tablename__ = "technical_debt"
+
+    id: Mapped[uuid.UUID] = mapped_column(
+        UUID(as_uuid=True), primary_key=True, default=new_uuid
+    )
+    td_id: Mapped[str | None] = mapped_column(
+        String(30), nullable=True, unique=True, index=True
+    )  # human-readable ref, e.g. TD-CUST-001
+    domain: Mapped[str] = mapped_column(String(50), nullable=False, index=True)
+    title: Mapped[str] = mapped_column(String(255), nullable=False)
+    description: Mapped[str | None] = mapped_column(Text, nullable=True)
+    location: Mapped[str | None] = mapped_column(String(500), nullable=True)
+    debt_type: Mapped[str] = mapped_column(
+        String(50), nullable=False, default="other"
+    )  # design | implementation | test | docs | dependencies | performance | security | other
+    severity: Mapped[str] = mapped_column(String(20), nullable=False, default="medium")
+    status: Mapped[TDStatus] = mapped_column(
+        Enum(TDStatus, name="tdstatus"), nullable=False, default=TDStatus.open
+    )
+    topic_id: Mapped[uuid.UUID | None] = mapped_column(
+        UUID(as_uuid=True), ForeignKey("topics.id", ondelete="SET NULL"), nullable=True
+    )
+    workstream_id: Mapped[uuid.UUID | None] = mapped_column(
+        UUID(as_uuid=True), ForeignKey("workstreams.id", ondelete="SET NULL"), nullable=True
+    )
+
+    topic: Mapped["Topic"] = relationship("Topic", lazy="selectin")  # noqa: F821
+    workstream: Mapped["Workstream"] = relationship("Workstream", lazy="selectin")  # noqa: F821