Introduce sphere-scoped labels (name, description, color) that replace the hardcoded feature request categories and add categorization to kanban tasks. - New `sphere_labels` and `entity_labels` tables with migration that converts existing categories into labels - CRUD API for labels at sphere level, gated by `manageLabels` permission - Labels on feature requests and kanban tasks (create, update, display) - Cross-sphere label injection prevention via sphere ownership validation - Shared LabelBadge and LabelPicker components - Admin label management page with color picker and delete confirmation - Entity label cleanup on cascade delete Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>