Implement State Hub v0.2: dependency graph, next-steps suggestions, design boundary

S0 — Design boundary formalised across all integration surfaces:
- TOOLS.md restructured with Design Boundary section, Sanctioned Write Tools,
  and Bootstrap-Only Tools (create_workstream, create_task) with explicit note
- project_claude_md.template and railiance CLAUDE.md updated with boundary note
  and get_next_steps() in session start protocol
- Global ~/.claude/CLAUDE.md updated accordingly

S1 — Workstream dependency graph:
- WorkstreamDependency model (directed edge, CASCADE on delete, unique pair constraint)
- Alembic migration 0b547c153153; script.py.mako added (was missing)
- REST API: POST/GET /workstreams/{id}/dependencies/, DELETE …/{dep_id} (hard delete)
- StateSummary open_workstreams enriched with depends_on/blocks lists
- MCP tools: create_dependency(), list_dependencies()
- Dashboard workstreams page: Dependencies section with relationship cards
- Seeded: custodian-agent-runtime → llm-shared-library + phase-0-operational-baseline

S2 — Suggesting Next Steps (sanctioned write use case #2):
- GET /state/next_steps derives suggestions from recently resolved decisions
  (→ first open task in same workstream) and cleared dependencies
  (→ first todo task in now-unblocked workstream)
- StateSummary.next_steps included on every summary call
- MCP tool: get_next_steps()
- Dashboard: "What's next?" card grid above Registered Projects

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

api/schemas/state.py

@@ -1,3 +1,4 @@
+import uuid
 from datetime import datetime
 
 from pydantic import BaseModel
@@ -6,7 +7,7 @@ from api.schemas.decision import DecisionRead
 from api.schemas.progress_event import ProgressEventRead
 from api.schemas.task import TaskRead
 from api.schemas.topic import TopicWithWorkstreams
-from api.schemas.workstream import WorkstreamWithTaskCounts
+from api.schemas.workstream import WorkstreamWithDeps
 
 
 class TopicTotals(BaseModel):
@@ -48,6 +49,23 @@ class Totals(BaseModel):
     decisions: DecisionTotals
 
 
+class NextStep(BaseModel):
+    """A derived suggestion pointing to where work should happen next.
+
+    Suggestions are never persisted — they are computed on demand from
+    current hub state: recently resolved decisions, newly unblocked tasks,
+    cleared dependencies.
+    """
+    type: str          # unblocked_task | resolved_decision | dependency_cleared
+    domain: str | None = None
+    workstream_id: uuid.UUID | None = None
+    workstream_title: str | None = None
+    workstream_slug: str | None = None
+    task_id: uuid.UUID | None = None
+    task_title: str | None = None
+    message: str       # plain-language explanation
+
+
 class StateSummary(BaseModel):
     generated_at: datetime
     totals: Totals
@@ -55,4 +73,5 @@ class StateSummary(BaseModel):
     blocking_decisions: list[DecisionRead]
     blocked_tasks: list[TaskRead]
     recent_progress: list[ProgressEventRead]
-    open_workstreams: list[WorkstreamWithTaskCounts]
+    open_workstreams: list[WorkstreamWithDeps]
+    next_steps: list[NextStep] = []