File formats: PostScript (.ps) and .epsf files open and place

The EPS reader read PostScript by any name, but the Open and Place
dialogs hid .ps and .epsf files, and a .ps or .epsf file whose header
is only %! could not be opened or placed ("not a format VectorCraft
reads"). The reference app lists .eps, .epsf and .ps under Open and
Place.

- A read-only PostScript format (ps) joins the format table. A .ps
  file opens and places through the EPS reader and reports the
  ps format. document.export does not write .ps; file.print does.
- .epsf is an EPS extension.
- OPEN_EXTS and PLACE_EXTS list epsf and ps, so the dialogs, the CLI
  help and the MCP open_file description list them.
  UNASSOCIATED_EXTS lists them too: the macOS bundle declares neither.
- A .ps or .epsf file whose header is only %! now pastes as EPS when
  copied in a file manager, as one with a %!PS header already did, and
  clipboard.importEps reads PostScript whose header is only %!, which
  it rejected before.

Docs: docs/mcp.md, docs/file-format-parity.md (.ps row),
docs/target-app-parity.md.

crates/engine/tests/import_fuzz.rs

@@ -1641,6 +1641,20 @@ proptest! {
         r.map_err(|msg| TestCaseError::fail(format!("placing hostile PostScript panicked: {msg}")))?;
     }
 
+    /// Hostile PostScript programs in `.ps` files whose header is only `%!`: opened, placed, and
+    /// pasted as a copied file is.
+    #[test]
+    fn ps_hostile_programs_never_panic(tokens in prop::collection::vec(arb_ps_token(), 0..60)) {
+        let ps = format!("%!\n{}\nshowpage\n", tokens.join(" "));
+        survive("hostile .ps", || vectorcraft_engine::cmd::fileio::load("x.ps", ps.as_bytes()).ok().map(|l| l.doc))?;
+        let r = catch_quiet(|| {
+            let mut s = rich_session();
+            let _ = no_panic(s.execute("file.place", &json!({"name": "x.ps", "dataBase64": vectorcraft_format::base64_encode(ps.as_bytes())})));
+        });
+        r.map_err(|msg| TestCaseError::fail(format!("placing a hostile .ps panicked: {msg}")))?;
+        paste_from_elsewhere("clipboard.importEps", json!({"dataBase64": vectorcraft_format::base64_encode(ps.as_bytes())}))?;
+    }
+
     /// Damaged or hostile CMYK images (a CMYK JPEG, an image with a key color): read as images,
     /// or as an error.
     #[test]