fix(deps): improve parent-child dependency UX (GH #440)

- Fix DEPENDENCIES.md: correct parent-child syntax (child depends on parent)
- Update bd show: display Children instead of Blocks for parent-child deps
- Group dependents by type with distinct labels

Generated with Claude Code

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

.beads/metadata.json

@@ -2,4 +2,4 @@
   "database": "beads.db",
   "jsonl_export": "issues.jsonl",
   "last_bd_version": "0.27.2"
-}
+}