chore: drop tool-name markers from source comments

Seventeen comments opened with a tag naming the tool that wrote them.
The tag goes and each comment keeps its reasoning, now starting as a
plain sentence. None of the reasoning changes.

The AGENTS.md note in .gitignore drops the story of how the file got
into the tree and keeps the one fact a reader needs: its advice to run
go fmt is destructive on this CRLF working tree.

Comments only; no code, build or test changes.

internal/updater/gatherer_host.go

@@ -114,7 +114,7 @@ func velocityJarVersion(path string) (updates.Version, error) {
 
 // manifestAttr returns one attribute value from a jar's META-INF/MANIFEST.MF.
 //
-// ponytail: this does not implement the JAR spec's 72-byte line folding (a wrapped
+// This does not implement the JAR spec's 72-byte line folding (a wrapped
 // value continues on the next line after a single leading space). Version values are
 // far short of the wrap point, so folding cannot bite here; if this ever reads a long
 // attribute, join continuation lines before splitting on ':'.