feat(fls): import host file systems into the model

importProject turns a PC's or notebook's Java file tree into Swift's
virtual file system, as Swift's registerVirtualFileSystem does: images
by type or extension from Base64, text by type, unknown types as binary
data or text, unsafe names and collisions left out with a warning, and
the whole import rejected over the project quota. NSString.pathExtension
is measured in the oracle, which now writes every imported file system.

On the 13 files Swift reads completely every file matches, images
compared by hash. Intended: a host whose file has no file system stays
empty, as in Java, where Swift adds the demo files of a new device.
Pending the applications step, the comparison reads our /webserver as
Swift's /www and leaves out the e-mail and Gnutella state files.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

packages/core/test/strings.swift.json

@@ -2253,6 +2253,24 @@
     "äöü",
     "k"
   ],
+  "pathExtension" : [
+    "txt",
+    "gz",
+    "",
+    "",
+    "",
+    "png",
+    "PNG",
+    "b",
+    "c d",
+    "",
+    "y",
+    "html",
+    "",
+    "",
+    "b",
+    "PNG"
+  ],
   "sort" : [
     [
       "B",