Implement bd-10: Export/import dependencies in JSONL

Added dependency support to export/import workflow:

Changes:
- Added GetDependencyRecords() to Storage interface to get raw dependency records
- Extended Issue struct with Dependencies field (omitempty for backward compat)
- Modified export.go to populate dependencies for each issue
- Modified import.go to process dependencies in second pass after all issues exist
- All tests pass

Benefits:
- JSONL is now self-contained with full dependency information
- Enables proper collision resolution in future (bd-12+)
- Idempotent imports: existing dependencies are not duplicated
- Forward references handled: dependencies created after all issues exist

Example output:
{
  "id": "bd-10",
  "title": "...",
  "dependencies": [{
    "issue_id": "bd-10",
    "depends_on_id": "bd-9",
    "type": "parent-child",
    "created_at": "...",
    "created_by": "stevey"
  }]
}

Closes bd-10

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

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

cmd/bd/export.go

@@ -48,6 +48,16 @@ Output to stdout by default, or use -o flag for file output.`,
 			return issues[i].ID < issues[j].ID
 		})
 
+		// Populate dependencies for each issue
+		for _, issue := range issues {
+			deps, err := store.GetDependencyRecords(ctx, issue.ID)
+			if err != nil {
+				fmt.Fprintf(os.Stderr, "Error getting dependencies for %s: %v\n", issue.ID, err)
+				os.Exit(1)
+			}
+			issue.Dependencies = deps
+		}
+
 		// Open output
 		out := os.Stdout
 		if output != "" {

cmd/bd/import.go

@@ -47,6 +47,7 @@ Behavior:
 		scanner := bufio.NewScanner(in)
 
 		var created, updated, skipped int
+		var allIssues []*types.Issue // Store all issues for dependency processing
 		lineNum := 0
 
 		for scanner.Scan() {
@@ -65,6 +66,9 @@ Behavior:
 				os.Exit(1)
 			}
 
+			// Store for dependency processing later
+			allIssues = append(allIssues, &issue)
+
 			// Check if issue exists
 			existing, err := store.GetIssue(ctx, issue.ID)
 			if err != nil {
@@ -121,11 +125,59 @@ Behavior:
 			os.Exit(1)
 		}
 
+		// Second pass: Process dependencies
+		// Do this after all issues are created to handle forward references
+		var depsCreated, depsSkipped int
+		for _, issue := range allIssues {
+			if len(issue.Dependencies) == 0 {
+				continue
+			}
+
+			for _, dep := range issue.Dependencies {
+				// Check if dependency already exists
+				existingDeps, err := store.GetDependencyRecords(ctx, dep.IssueID)
+				if err != nil {
+					fmt.Fprintf(os.Stderr, "Error checking dependencies for %s: %v\n", dep.IssueID, err)
+					os.Exit(1)
+				}
+
+				// Skip if this exact dependency already exists
+				exists := false
+				for _, existing := range existingDeps {
+					if existing.DependsOnID == dep.DependsOnID && existing.Type == dep.Type {
+						exists = true
+						break
+					}
+				}
+
+				if exists {
+					depsSkipped++
+					continue
+				}
+
+				// Add dependency
+				if err := store.AddDependency(ctx, dep, "import"); err != nil {
+					// Ignore errors for missing target issues or cycles
+					// This can happen if dependencies reference issues not in the import
+					fmt.Fprintf(os.Stderr, "Warning: could not add dependency %s → %s: %v\n",
+						dep.IssueID, dep.DependsOnID, err)
+					continue
+				}
+				depsCreated++
+			}
+		}
+
 		// Print summary
 		fmt.Fprintf(os.Stderr, "Import complete: %d created, %d updated", created, updated)
 		if skipped > 0 {
 			fmt.Fprintf(os.Stderr, ", %d skipped", skipped)
 		}
+		if depsCreated > 0 || depsSkipped > 0 {
+			fmt.Fprintf(os.Stderr, ", %d dependencies added", depsCreated)
+			if depsSkipped > 0 {
+				fmt.Fprintf(os.Stderr, " (%d already existed)", depsSkipped)
+			}
+		}
 		fmt.Fprintf(os.Stderr, "\n")
 	},
 }