feat(state-hub): v0.3 schema — contributions + sbom_entries migrations, models, schemas, routers

Migrations (chain: b1c2d3e4f5a6 → c2d3e4f5a6b7 → d3e4f5a6b7c8):
- c2d3e4f5a6b7: contributions table (contributiontype BR/FR/EP/UPR enum,
  contributionstatus 7-state lifecycle, FKs to topics/workstreams)
- d3e4f5a6b7c8: sbom_entries table (ecosystem enum, snapshot-based replacement),
  + sbom_source + last_sbom_at columns on managed_repos

New models: Contribution (ContributionType, ContributionStatus), SBOMEntry (Ecosystem)
Modified: ManagedRepo (sbom_source, last_sbom_at columns)

New routers:
- /contributions/ — CRUD + lifecycle-guarded PATCH /status + soft-delete (withdrawn)
- /sbom/ — ingest (replace snapshot), list, per-repo view, licence report

Modified:
- /state/summary now includes contribution_counts and licence_risk_count
- main.py: registers contributions + sbom routers; bumps version to 0.6.0

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

api/models/__init__.py

@@ -9,6 +9,8 @@ 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
+from api.models.contribution import Contribution, ContributionType, ContributionStatus
+from api.models.sbom_entry import SBOMEntry, Ecosystem
 
 __all__ = [
     "Base",
@@ -22,4 +24,6 @@ __all__ = [
     "ExtensionPoint", "EPStatus",
     "TechnicalDebt", "TDStatus",
     "ManagedRepo",
+    "Contribution", "ContributionType", "ContributionStatus",
+    "SBOMEntry", "Ecosystem",
 ]