Skeleton, mnemonic input, derivation, and the ssh pub and priv commands (closes #1)

The module, the script entrypoints and Makefile, Docker-only linting, the mnemonic sources in the specified order with their refusals, the BIP-85 derivation, and keyfunc ssh pub and priv with the README test vectors as tests. Two review rounds; the second passed with no findings.

Model: opus-5 (implementation and review); fable-5-1 (landing)

go.mod

@@ -0,0 +1,26 @@
+module git.eeqj.de/sneak/keyfunc
+
+go 1.26
+
+require (
+	git.eeqj.de/sneak/secret v0.0.0-20260810132333-41cea400a7fd
+	github.com/btcsuite/btcd v0.24.2
+	github.com/btcsuite/btcd/btcutil v1.1.6
+	github.com/spf13/cobra v1.9.1
+	github.com/stretchr/testify v1.8.4
+	github.com/tyler-smith/go-bip39 v1.1.0
+	golang.org/x/crypto v0.38.0
+	golang.org/x/term v0.32.0
+)
+
+require (
+	github.com/btcsuite/btcd/btcec/v2 v2.1.3 // indirect
+	github.com/btcsuite/btcd/chaincfg/chainhash v1.1.0 // indirect
+	github.com/davecgh/go-spew v1.1.1 // indirect
+	github.com/decred/dcrd/dcrec/secp256k1/v4 v4.0.1 // indirect
+	github.com/inconshreveable/mousetrap v1.1.0 // indirect
+	github.com/pmezard/go-difflib v1.0.0 // indirect
+	github.com/spf13/pflag v1.0.6 // indirect
+	golang.org/x/sys v0.33.0 // indirect
+	gopkg.in/yaml.v3 v3.0.1 // indirect
+)