`secret rm ..` deleted the whole vault; `secret rm .` and `secret rm ""`
deleted every secret. rm, mv, the version commands, encrypt and decrypt
built paths from the name unchecked; import checked it only after
reading the source file.
Each now calls vault.ValidateSecretName, which wraps the existing rule,
on the name as given, before building any path; MoveSecret checks both
names before switching the current vault. Its error and README.md state
the rule. The test-only copy of the rule in internal/secret is removed.
The regression test runs each rejected command on a copy of two
in-memory vaults and requires the exact error and an unchanged state
directory.
Model: opus-5-5