deps: add bluemonday HTML sanitizer

Add github.com/microcosm-cc/bluemonday for safe HTML sanitization.
This library is industry-standard, actively maintained, and has zero
telemetry/network calls.

License: BSD-3-Clause (compatible with project's GPL-3 license)
Used for sanitizing book description HTML before rendering.

go.mod

@@ -33,6 +33,7 @@ require (
 
 require (
 	github.com/alecthomas/chroma v0.10.0 // indirect
+	github.com/aymerick/douceur v0.2.0 // indirect
 	github.com/clipperhouse/uax29/v2 v2.7.0 // indirect
 	github.com/davecgh/go-spew v1.1.2-0.20180830191138-d8f796af33cc // indirect
 	github.com/dlclark/regexp2 v1.11.5 // indirect
@@ -40,6 +41,7 @@ require (
 	github.com/go-playground/locales v0.14.1 // indirect
 	github.com/go-playground/universal-translator v0.18.1 // indirect
 	github.com/google/go-cmp v0.7.0 // indirect
+	github.com/gorilla/css v1.0.1 // indirect
 	github.com/hhrutter/lzw v1.0.0 // indirect
 	github.com/hhrutter/pkcs7 v0.2.0 // indirect
 	github.com/hhrutter/tiff v1.0.2 // indirect
@@ -49,6 +51,7 @@ require (
 	github.com/kr/pretty v0.3.1 // indirect
 	github.com/leodido/go-urn v1.4.0 // indirect
 	github.com/mattn/go-runewidth v0.0.21 // indirect
+	github.com/microcosm-cc/bluemonday v1.0.27 // indirect
 	github.com/pkg/errors v0.9.1 // indirect
 	github.com/pmezard/go-difflib v1.0.1-0.20181226105442-5d4384ee4fb2 // indirect
 	github.com/rogpeppe/go-internal v1.14.1 // indirect