Language detection: switch to go-enry with hint-seeded classifier (#41)

- Add github.com/go-enry/go-enry/v2 dependency to go.mod
- guessLang: JSON fast path, then enry strategies (shebangs, XML, modelines,
  content heuristics), then enry's Linguist-trained Bayesian classifier over
  regex-hint candidate languages; curated dropdown expanded with typescript,
  html, css, xml, php, ruby, perl, lua, dockerfile, toml, ini, diff, csharp
- enry display names normalized to lowercase stored ids (Dockerfile->dockerfile,
  Shell->bash, C#->csharp); unsupported languages render unhighlighted
- Tests: existing languages, all new languages, magic markers (enry shebang/
  DOCTYPE/FROM/diff handling), canonical mapping

go.mod

@@ -4,12 +4,14 @@ go 1.27.1
 
 require (
 	github.com/go-chi/chi/v5 v5.3.2
+	github.com/go-enry/go-enry/v2 v2.9.6
 	golang.org/x/crypto v0.39.0
 	modernc.org/sqlite v1.58.0
 )
 
 require (
 	github.com/dustin/go-humanize v1.0.1 // indirect
+	github.com/go-enry/go-oniguruma v1.2.1 // indirect
 	github.com/google/uuid v1.6.0 // indirect
 	github.com/mattn/go-isatty v0.0.24 // indirect
 	github.com/ncruces/go-strftime v1.0.0 // indirect