Move the CLI to urfave/cli v3 (closes #110)

Ported per the library's v2-to-v3 migration guide: the app is a root
cli.Command, actions take a context and the command, and flag environment
variables become value sources. -v, -q and the version flag are marked
local so that, as before, only the commands that define them accept them.
go mod tidy raises testify to v1.12.1, which v3 requires. The
urfave_cli_no_docs build tag is dropped from script/build and the
Dockerfile; v3 has no such tag. v3 no longer refuses a flag given under
two of its names, so -v --verbose now gives debug output, and the test
that pinned the refusal becomes a TestVerboseCount case. Help text follows
v3's templates.

Model: opus-5-5

go.mod

@@ -9,27 +9,21 @@ require (
 	github.com/klauspost/compress v1.18.2
 	github.com/multiformats/go-multihash v0.2.3
 	github.com/spf13/afero v1.8.0
-	github.com/stretchr/testify v1.8.1
-	github.com/urfave/cli/v2 v2.27.7
+	github.com/stretchr/testify v1.12.1
+	github.com/urfave/cli/v3 v3.14.0
 	golang.org/x/term v0.0.0-20210927222741-03fcf44c2211
 	google.golang.org/protobuf v1.28.1
 )
 
 require (
-	github.com/cpuguy83/go-md2man/v2 v2.0.7 // indirect
 	github.com/klauspost/cpuid/v2 v2.0.9 // indirect
-	github.com/kr/pretty v0.2.0 // indirect
 	github.com/minio/sha256-simd v1.0.0 // indirect
 	github.com/mr-tron/base58 v1.2.0 // indirect
 	github.com/multiformats/go-varint v0.0.6 // indirect
-	github.com/pmezard/go-difflib v1.0.0 // indirect
-	github.com/russross/blackfriday/v2 v2.1.0 // indirect
 	github.com/spaolacci/murmur3 v1.1.0 // indirect
-	github.com/xrash/smetrics v0.0.0-20240521201337-686a1a2994c1 // indirect
+	go.yaml.in/yaml/v3 v3.0.5 // indirect
 	golang.org/x/crypto v0.0.0-20220525230936-793ad666bf5e // indirect
 	golang.org/x/sys v0.1.0 // indirect
 	golang.org/x/text v0.3.6 // indirect
-	gopkg.in/check.v1 v1.0.0-20190902080502-41f04d3bba15 // indirect
-	gopkg.in/yaml.v3 v3.0.1 // indirect
 	lukechampine.com/blake3 v1.1.6 // indirect
 )