059990fce4
The save-regression cherry-pick (4b5812a) re-introduced the pre-refactor
vault.rs alongside vault/mod.rs, causing E0761 (ambiguous module) on CI.
vault/mod.rs (from PR #21 refactor-vault-rs) is the correct implementation
and already exports all needed functions (save_note_content, get_note_content,
purge_trash, etc.). Removing the duplicate vault.rs resolves the CI failure.
