Rename the Go module to sneak.berlin/go/secret (closes #43)

REPO_POLICIES.md requires the module root sneak.berlin/go/<name>.
go.mod, every import (rewritten with gofmt -r), the -X flags in
script/build and the examples in the pkg READMEs now use the new path.
go mod tidy lists go-humanize and fatih/color as direct requirements,
since internal/cli imports them.

This breaks anyone who fetched or imported git.eeqj.de/sneak/secret:
they must switch to sneak.berlin/go/secret, which resolves to this
repository.

Model: opus-5-5

go.mod

@@ -1,4 +1,4 @@
-module git.eeqj.de/sneak/secret
+module sneak.berlin/go/secret
 
 go 1.24.1
 
@@ -10,6 +10,8 @@ require (
 	github.com/btcsuite/btcd/btcutil v1.1.6
 	github.com/btcsuite/btcutil v0.0.0-20190425235716-9e5f4b9a998d
 	github.com/creack/pty v1.1.24
+	github.com/dustin/go-humanize v1.0.1
+	github.com/fatih/color v1.18.0
 	github.com/keybase/go-keychain v0.0.0-20230307172405-3e4884637dd1
 	github.com/oklog/ulid/v2 v2.1.1
 	github.com/spf13/afero v1.14.0
@@ -26,8 +28,6 @@ require (
 	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/dustin/go-humanize v1.0.1 // indirect
-	github.com/fatih/color v1.18.0 // indirect
 	github.com/inconshreveable/mousetrap v1.1.0 // indirect
 	github.com/mattn/go-colorable v0.1.13 // indirect
 	github.com/mattn/go-isatty v0.0.20 // indirect