fix(merge): proper 3-way merge for dependencies - removals win (bd-ndye)

CRITICAL: Fixed dependency resurrection bug that caused removed/orphaned
dependencies to keep coming back after sync.

Root cause: mergeDependencies() was doing a union (additive only) and
completely ignored the base parameter. This meant any dependency present
in either left or right would be included, even if it was intentionally
removed.

Fix: Proper 3-way merge where REMOVALS ARE AUTHORITATIVE:
- If dep was in base and removed by left OR right → stays removed
- If dep wasn't in base and added by left OR right → included
- If dep was in base and both still have it → included

This fixes months of issues with orphaned parent-child relationships
being resurrected during git sync operations.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

cmd/bd/info.go

@@ -293,6 +293,7 @@ var versionChanges = []VersionChange{
 		Changes: []string{
 			"bd graph command shows dependency counts using subgraph formatting (bd-6v2)",
 			"types.StatusPinned for persistent beads that survive cleanup",
+			"CRITICAL: Fixed dependency resurrection bug in 3-way merge (bd-ndye) - removals now win",
 		},
 	},
 	{