fix: CI test failures and lint errors

- Fixed test file naming: issues.jsonl -> beads.jsonl
  - beads_test.go: Update expected path in TestFindJSONLPath
  - internal/beads/beads_test.go: Update TestFindJSONLPathDefault
  - cmd/bd/main_test.go: Update TestAutoFlushJSONLContent

- Fixed lint errors (gosec):
  - G304: Added nosec comments for file operations with user-provided paths
  - G204: Added nosec comment for subprocess with controlled binary path

- Fixed lint errors (errcheck):
  - cmd/bd/test_wait_helper.go: Acknowledge error return values with _
  - cmd/bd/onboard.go: Handle fmt.Fprintf error return

All tests passing locally. All lint checks passing.

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

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

internal/beads/beads_test.go

@@ -168,9 +168,9 @@ func TestFindJSONLPathDefault(t *testing.T) {
 	// Create a fake database path (no .jsonl files exist)
 	dbPath := filepath.Join(tmpDir, "test.db")
 
-	// Should return default issues.jsonl
+	// Should return default beads.jsonl
 	result := FindJSONLPath(dbPath)
-	expected := filepath.Join(tmpDir, "issues.jsonl")
+	expected := filepath.Join(tmpDir, "beads.jsonl")
 	if result != expected {
 		t.Errorf("Expected '%s', got '%s'", expected, result)
 	}