go-bip39 gone from go.mod and go.sum (#72)

What is on `next`, reviewed.

- go-bip39 is gone from `go.mod` and `go.sum`: keyfunc now requires `sneak/secret` at `ef0ae90`, the commit that gives `secret` its own copy (sneak/secret#130). No derived key, mnemonic or test vector changes.

To know before merging:

- `secret`'s module is now `sneak.berlin/go/secret` (sneak/secret#43), so keyfunc's requirement, its two imports of `secret`'s `bip85` package and one README sentence use that path. The Go module proxy serves that path, so `go install` keeps working.

Model: opus-5-5
Reviewed-on: #72
Co-authored-by: clawbot <sneak+clawbot@sneak.cloud>

go.sum

@@ -4,8 +4,6 @@ filippo.io/age v1.3.2 h1:r6RSZLFSMm6rzKepZ7ZAYkKCu14f3/Me8c7uKYh7C8c=
 filippo.io/age v1.3.2/go.mod h1:TH/Yr2sSRhCKbaH4XPxpUV0Us8Gv6txYUpiZQWz8Evk=
 filippo.io/hpke v0.4.0 h1:p575VVQ6ted4pL+it6M00V/f2qTZITO0zgmdKCkd5+A=
 filippo.io/hpke v0.4.0/go.mod h1:EmAN849/P3qdeK+PCMkDpDm83vRHM5cDipBJ8xbQLVY=
-git.eeqj.de/sneak/secret v0.0.0-20260810132333-41cea400a7fd h1:6YFV6horz2wDFPWWhour8qx8gLGyO0qoplwEeOuQ2J4=
-git.eeqj.de/sneak/secret v0.0.0-20260810132333-41cea400a7fd/go.mod h1:gKCcMZvlBOqusn/BxR8IyFmSJQr6R4vvjJ926iNpOSI=
 github.com/btcsuite/btcd v0.25.0 h1:JPbjwvHGpSywBRuorFFqTjaVP4y6Qw69XJ1nQ6MyWJM=
 github.com/btcsuite/btcd v0.25.0/go.mod h1:qbPE+pEiR9643E1s1xu57awsRhlCIm1ZIi6FfeRA4KE=
 github.com/btcsuite/btcd/btcec/v2 v2.5.0 h1:KioMXOWa76b86sTZZOmbzv/ldaQCmB8KFAyn5PbB8E8=
@@ -30,8 +28,6 @@ github.com/spf13/pflag v1.0.9 h1:9exaQaMOCwffKiiiYk6/BndUBv+iRViNW+4lEMi0PvY=
 github.com/spf13/pflag v1.0.9/go.mod h1:McXfInJRrz4CZXVZOBLb0bTZqETkiAhM9Iw0y3An2Bg=
 github.com/stretchr/testify v1.12.1 h1:EuwCh5fleGS7H32xRwO3wRGT7DxrDhLAT6FF8MpWDWE=
 github.com/stretchr/testify v1.12.1/go.mod h1:MDEgiDPPsNp5cuIrHPPCyornHKgEVbtFUmoNlxoYthg=
-github.com/tyler-smith/go-bip39 v1.1.0 h1:5eUemwrMargf3BSLRRCalXT93Ns6pQJIjYQN2nyfOP8=
-github.com/tyler-smith/go-bip39 v1.1.0/go.mod h1:gUYDtqQw1JS3ZJ8UWVcGTGqqr6YIN3CWg+kkNaLt55U=
 go.yaml.in/yaml/v3 v3.0.4/go.mod h1:DhzuOOF2ATzADvBadXxruRBLzYTpT36CKvDb3+aBEFg=
 go.yaml.in/yaml/v3 v3.0.5 h1:N6y/pJk8buWs9NY5ERU2HSMfm+IuD/OtfdAnq6kESPw=
 go.yaml.in/yaml/v3 v3.0.5/go.mod h1:HVTZu1O7/Vkt2N+BFy8Zza+lnLsABggaTM2ZpNIGuKg=
@@ -42,3 +38,5 @@ golang.org/x/sys v0.48.0/go.mod h1:hNLxWAXmnKAxqDtdwIYC4bM9oQPEecfsnNMuSxOs3og=
 golang.org/x/term v0.46.0 h1:3+OXuTbaKDgwk8jTi3aSLHRlmWqHEUDUtxnbFigO4YE=
 golang.org/x/term v0.46.0/go.mod h1:+K02xbkittuwc0Am4abfA3Fc+XRGXkvBXNO88NCXPoc=
 gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
+sneak.berlin/go/secret v0.0.0-20261007105610-ef0ae90768c8 h1:Bd2bUsRCN8xhcrpH3LpJqHxR2QffeOuF5z76iP4BFnw=
+sneak.berlin/go/secret v0.0.0-20261007105610-ef0ae90768c8/go.mod h1:uVx9ZuE7ZMIOBY2B1ElXCs97CTsEfuham3NQRdLj5lI=