External dependencies (external:project:capability) are now visible in
the dependency tree output. Previously they were invisible because the
recursive CTE only JOINed against the issues table.
Changes:
- GetDependencyTree now fetches external deps and adds them as synthetic
leaf nodes with resolution status (satisfied/blocked)
- formatTreeNode displays external deps with special formatting
- Added helper parseExternalRefParts for parsing external refs
Test coverage added for:
- External deps appearing in dependency tree
- Cycle detection ignoring external refs
- CheckExternalDep when target has no .beads directory
- Various invalid external ref format variations
Closes: bd-vks2, bd-mv6h, bd-d9mu
ad02b80330