feat(state-hub): implement v0.5 — dynamic domains & multi-repo

Replaces the hardcoded 6-domain PostgreSQL ENUM with a first-class
`domains` DB table, and adds a `managed_repos` table for multi-repo
support per domain.

P1 — Domain as a DB entity:
- Migration b1c2d3e4f5a6: creates `domains` table, migrates topics.domain
  ENUM column to domain_id FK, drops the domain ENUM type
- Domain ORM model (api/models/domain.py) + Pydantic schemas
- Domain API router: GET/POST /domains/, GET/PATCH /domains/{slug}/,
  rename and archive endpoints with EP/TD cascade on rename
- Topic model updated: domain_id FK + @property domain_slug for
  backwards-compatible JSON serialization (field renamed domain → domain_slug)
- TopicCreate/TopicRead updated; seed.py rewritten to use FK lookup

P2 — Multi-repo support:
- ManagedRepo ORM model (api/models/managed_repo.py) + schemas
- Repo API router: GET/POST /repos/, GET/PATCH /repos/{slug}/, archive
- Makefile: add-domain, rename-domain, add-repo, list-repos targets
- register_project.sh: verify domain via /domains/ API + POST /repos/

P3 — MCP tools & live validation:
- 6 new MCP tools: list_domains, create_domain, rename_domain,
  archive_domain, list_domain_repos, register_repo
- EP/TD routers: replace hardcoded VALID_DOMAINS set with per-request
  DB lookup — returns 422 with list of valid slugs on unknown domain
- State summary: adds domains: list[DomainSummary] (slug, name,
  repo_count, active_workstream_count, ep_count, td_count)
- TOOLS.md updated with domain management section

P4 — Dashboard:
- New domains.md page with KPI row + domain cards + repo lists
- domains.json.py + repos.json.py data loaders
- Domains page added to observablehq.config.js nav
- workstreams.md, extensions.md, techdept.md: domain_slug fix +
  dynamic domain list loaded from /domains/ API (no longer hardcoded)

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

api/models/__init__.py

@@ -1,5 +1,6 @@
 from api.models.base import Base
-from api.models.topic import Topic, TopicStatus, Domain
+from api.models.domain import Domain
+from api.models.topic import Topic, TopicStatus
 from api.models.workstream import Workstream, WorkstreamStatus
 from api.models.workstream_dependency import WorkstreamDependency
 from api.models.task import Task, TaskStatus, TaskPriority
@@ -7,10 +8,12 @@ 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
+from api.models.managed_repo import ManagedRepo
 
 __all__ = [
     "Base",
-    "Topic", "TopicStatus", "Domain",
+    "Domain",
+    "Topic", "TopicStatus",
     "Workstream", "WorkstreamStatus",
     "WorkstreamDependency",
     "Task", "TaskStatus", "TaskPriority",
@@ -18,4 +21,5 @@ __all__ = [
     "ProgressEvent",
     "ExtensionPoint", "EPStatus",
     "TechnicalDebt", "TDStatus",
+    "ManagedRepo",
 ]