fix: rename migration to sequential 068, document convention

Renamed fc01_add_pending_task_lane → 068_add_pending_task_lane with
revision ID "068" and down_revision "067". Added migration naming
convention to CLAUDE.md to prevent future hex-hash migrations.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

backend/alembic/versions/068_add_pending_task_lane.py

@@ -1,14 +1,14 @@
 """add pending_task_lane to ai_sessions
 
-Revision ID: fc01a1b2c3d4
-Revises: fb1481317ff6
+Revision ID: 068
+Revises: 067
 Create Date: 2026-03-27
 """
 from alembic import op
 import sqlalchemy as sa
 from sqlalchemy.dialects.postgresql import JSONB
 
-revision = "fc01a1b2c3d4"
+revision = "068"
 down_revision = "067"
 branch_labels = None
 depends_on = None