YAML frontmatter from the Rust CLI uses depends_on (snake_case) but the
TaskInput schema expects dependsOn (camelCase). Without normalization,
Value.Clean() strips the unknown key and dependencies are silently lost.
Add step 3.5 in parseFrontmatter: if depends_on is present and dependsOn
is not, remap the key before schema validation. If both are present,
dependsOn wins (camelCase is canonical).