fix(man): always ignore man sync test instead of feature-gating

The man(1) output varies across systems (different groff versions, line
breaking, etc.), so the man sync test cannot reliably pass in CI. Make
it always #[ignore] instead of gating on a man-test feature, and remove
the man-test feature entirely. The pdu.1.man file is a reference file
derived from pdu.1 (which IS sync-checked), so CI enforcement is not
needed.

https://claude.ai/code/session_01CrXuWDMVQsiUBoy6ceACsF

Author: claude

Cargo.toml

@@ -64,7 +64,6 @@ default = ["cli"]
 json = ["serde/derive", "serde_json"]
 cli = ["clap/derive", "clap_complete", "clap-utilities", "json"]
 cli-completions = ["cli"]
-man-test = []
 ai-instructions = ["clap/derive"]
 
 [dependencies]

tests/sync_man_page.rs

@@ -40,10 +40,7 @@ fn roff() {
 }
 
 #[test]
-#[cfg_attr(
-    not(feature = "man-test"),
-    ignore = "requires man(1); enable with --features man-test"
-)]
+#[ignore = "requires man(1); run with --include-ignored to check"]
 fn man() {
     check("man", "1");
 }