fix(scanner): pass filename hint to gotaglib's OpenStream for format detection (#5012)

* fix: split reflex -R flags to preserve directory exclusion optimization

Combining the _test.go exclusion pattern (which uses $) into the same -R
regex as the directory prefixes (^ui, ^data, ^db/migrations) disabled
reflex's ExcludePrefix optimization. Reflex disables prefix-based
directory skipping when the regex AST contains $, \z, or \b operators,
causing it to traverse into ui/node_modules and hit "too many open files".

Splitting into two separate -R flags fixes this: the directory prefix
regex remains $-free so ExcludePrefix works, while the _test.go pattern
gets its own flag where the $ anchor doesn't affect directory skipping.

* fix(gotaglib): pass filename hint to OpenStream for format detection

OpenStream relies on content-sniffing when no filename is provided,
which fails for some files (e.g. OPUS). Pass the filename via the new
WithFilename option so TagLib can use the file extension as a hint.

Also adds an OPUS test fixture and test entry.

Relates to https://github.com/navidrome/navidrome/issues/4604#issuecomment-3868569113, #4998, #5010

go.mod

@@ -7,7 +7,7 @@ replace (
 	github.com/dhowden/tag v0.0.0-20240417053706-3d75831295e8 => github.com/deluan/tag v0.0.0-20241002021117-dfe5e6ea396d
 
 	// Fork to implement raw tags support
-	go.senan.xyz/taglib => github.com/deluan/go-taglib v0.0.0-20260119020817-8753c7531798
+	go.senan.xyz/taglib => github.com/deluan/go-taglib v0.0.0-20260209170351-c057626454d0
 )
 
 require (