Add man pages for vault and every command

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

docs/vault-mv.1

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+.TH VAULT-MV 1 "September 2026" "vault" "User Commands"
+.SH NAME
+vault-mv \- rename a stored file
+.SH SYNOPSIS
+.B vault mv
+.RB [ \-\-key
+.IR PATH ]
+.RB [ \-\-vault
+.IR DIR ]
+.I OLD NEW
+.br
+.B vault rename
+\&...
+.SH DESCRIPTION
+Renames \fIOLD\fR to \fINEW\fR, which may be in another folder. Fails if
+\fINEW\fR exists or is not a valid vault path. File contents are not
+re-encrypted.
+.SH OPTIONS
+.TP
+.BI \-\-key " PATH"
+Key file. Default: $VAULT_KEY, else ~/.vault/key.
+.TP
+.BI \-\-vault " DIR"
+Vault directory. Default: $VAULT_DIR, else ~/.vault/store.
+.SH ENVIRONMENT
+.TP
+.B VAULT_PASSPHRASE
+Passphrase, instead of prompting on the terminal.
+.SH SEE ALSO
+.BR vault (1),
+.BR vault\-rm (1)
+.SH AUTHOR
+Andy Dixon <vault@dixon.cx>, https://www.dixon.cx