Recover user files from orphaned state-vN.bin after a version bump (#365)

* Detect orphaned state-vN.bin and offer file recovery to a host folder

When STATE_VERSION is bumped, users previously lost their C:\ silently.
The Welcome card now detects an older state file (v4+), explains what
happened, and offers a one-click recovery: spin up a throwaway v86
(no boot), restore the legacy state to populate the hda dirty-block
overlay, walk the FAT32 tree reading overlay-if-dirty-else-base, and
copy any file the guest ever wrote out to ~/Downloads/Recovered C Drive.

Directories are created lazily so empty branches never appear; success
and failure render in the panel (no native dialogs). The geometry
constraint that keeps overlay+new-base valid is documented next to
STATE_VERSION. Also makes the dev-mode CDP port overridable via
WIN95_DEBUG_PORT so worktree instances don't fight over 9222.

* prettier

src/css/start.css

@@ -80,6 +80,24 @@
   }
 }
 
+.welcome-warn {
+  background: #fff;
+
+  p {
+    margin: 0 0 8px;
+  }
+
+  .welcome-warn-buttons {
+    display: flex;
+    gap: 6px;
+    margin-top: 4px;
+
+    button {
+      height: 24px;
+    }
+  }
+}
+
 .welcome-actions {
   width: 130px;
   display: flex;