feat: implement conditional bond type for mol bond (bd-kzda)

Conditional bonds now work as documented: "B runs only if A fails".

Implementation:
- Add DepConditionalBlocks dependency type to types.go
- Add IsFailureClose() helper to detect failure keywords in close_reason
- Update blocked cache to handle conditional-blocks:
  - B is blocked while A is open
  - B stays blocked if A closes with success
  - B becomes unblocked if A closes with failure

Failure keywords: failed, rejected, wontfix, cancelled, abandoned,
blocked, error, timeout, aborted (case-insensitive)

Updated bondProtoProto, bondProtoMol, bondMolMol to use
DepConditionalBlocks for conditional bond type.

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

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

beads.go

@@ -92,10 +92,11 @@ const (
 
 // DependencyType constants
 const (
-	DepBlocks         = types.DepBlocks
-	DepRelated        = types.DepRelated
-	DepParentChild    = types.DepParentChild
-	DepDiscoveredFrom = types.DepDiscoveredFrom
+	DepBlocks            = types.DepBlocks
+	DepRelated           = types.DepRelated
+	DepParentChild       = types.DepParentChild
+	DepDiscoveredFrom    = types.DepDiscoveredFrom
+	DepConditionalBlocks = types.DepConditionalBlocks // B runs only if A fails (bd-kzda)
 )
 
 // SortPolicy constants