feat(token-tracking): record AI token consumption per task (CUST-WP-0029)

Introduces end-to-end token consumption tracking so agent work is
visible as a cost/effort metric alongside tasks and workplans.

- Migration o2j3k4l5m6n7: token_events table with FK indexes on
  task_id, workstream_id, repo_id, created_at
- ORM model, Pydantic schemas (TokenEventCreate, TokenEventRead with
  computed tokens_total, TokenSummary)
- Router: POST /token-events/, GET /token-events/ (7 filters),
  GET /token-events/summary/ (task|workstream|repo|commit|release scope)
- MCP tools: record_token_event, get_token_summary (formatted table)
- update_task_status enriched with optional tokens_in/tokens_out
  passthrough — one call creates status update + token event
- Dashboard token-cost.md page: by-repo bar, by-workplan table,
  by-model bar, top-10 tasks by tokens
- ralph-workplan skill updated with token reporting guidance and
  per-task heuristics for estimating counts
- Tests: test_token_events.py + test_token_passthrough.py (182 pass)

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

api/routers/tasks.py

@@ -7,6 +7,7 @@ from sqlalchemy.ext.asyncio import AsyncSession
 
 from api.database import get_session
 from api.models.task import Task, TaskStatus
+from api.models.token_event import TokenEvent
 from api.schemas.task import TaskCreate, TaskRead, TaskUpdate
 
 router = APIRouter(prefix="/tasks", tags=["tasks"])
@@ -72,10 +73,33 @@ async def update_task(
     task = await session.get(Task, task_id)
     if task is None:
         raise HTTPException(status_code=404, detail="Task not found")
-    for field, value in body.model_dump(exclude_unset=True).items():
+
+    # Separate token fields from task fields
+    token_fields = {"tokens_in", "tokens_out", "model", "agent", "session_id"}
+    update_data = body.model_dump(exclude_unset=True)
+    token_data = {k: update_data.pop(k) for k in list(update_data.keys()) if k in token_fields}
+
+    for field, value in update_data.items():
         setattr(task, field, value)
     await session.commit()
     await session.refresh(task)
+
+    # Create token event if token passthrough fields provided
+    if "tokens_in" in token_data and "tokens_out" in token_data:
+        event = TokenEvent(
+            task_id=task_id,
+            workstream_id=task.workstream_id,
+            tokens_in=token_data["tokens_in"],
+            tokens_out=token_data["tokens_out"],
+            model=token_data.get("model"),
+            agent=token_data.get("agent"),
+            session_id=token_data.get("session_id"),
+            ref_type="task",
+            ref_id=str(task_id),
+        )
+        session.add(event)
+        await session.commit()
+
     return task