fix: resolve golangci-lint warnings

- Handle ignored errors with explicit _ assignment (errcheck)
- Add #nosec comments for false positive G304/G204 warnings (gosec)
- Fix misspelling: cancelled -> canceled

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

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

cmd/bd/compact.go

@@ -1019,7 +1019,7 @@ func pruneExpiredTombstones() (*TombstonePruneResult, error) {
 		}
 		allIssues = append(allIssues, &issue)
 	}
-	file.Close()
+	_ = file.Close() // Best effort close, already read all data
 
 	// Determine TTL
 	ttl := types.DefaultTombstoneTTL
@@ -1052,20 +1052,20 @@ func pruneExpiredTombstones() (*TombstonePruneResult, error) {
 	encoder := json.NewEncoder(tempFile)
 	for _, issue := range kept {
 		if err := encoder.Encode(issue); err != nil {
-			tempFile.Close()
-			os.Remove(tempPath)
+			_ = tempFile.Close()
+			_ = os.Remove(tempPath) // Best effort cleanup
 			return nil, fmt.Errorf("failed to write issue %s: %w", issue.ID, err)
 		}
 	}
 
 	if err := tempFile.Close(); err != nil {
-		os.Remove(tempPath)
+		_ = os.Remove(tempPath) // Best effort cleanup
 		return nil, fmt.Errorf("failed to close temp file: %w", err)
 	}
 
 	// Atomically replace
 	if err := os.Rename(tempPath, issuesPath); err != nil {
-		os.Remove(tempPath)
+		_ = os.Remove(tempPath) // Best effort cleanup
 		return nil, fmt.Errorf("failed to replace issues.jsonl: %w", err)
 	}