fix(flr): resolve guest paths into the FLR partition namespace

zerto_recover_file passed the guest absolute path straight to
POST /v1/flrs/{session}/download, which the ZVM rejects:

  HTTP 400 {"Message":"Invalid path: check location exists or
  correct path syntax."}

FLR browse/download is rooted at partitions, not the guest's /.
/home/justin/app-config.yaml is Volume2-Ext4/home/justin/app-config.yaml.
server.py already called browse_flr() but discarded the result, so
nothing ever resolved the path.

Add resolve_flr_path() and browsable_partitions() to recover.py:

- browse path "" returns {MainPathItem, PathItems}, not a bare list
- skip partitions with IsBrowsable false. A Linux guest reports
  Volume1-Unknown as "Cannot restore. Partition type Unknown is not
  supported." Do not assume the first partition is the right one.
- browse returns child paths percent-encoded
  (Volume2-Ext4%2fhome%2fjustin%2fapp-config.yaml); download wants
  them decoded with plain slashes
- raise a ZertoError naming what was searched when the file is
  absent, since "not replicated into that checkpoint yet" is the
  likely cause and is actionable

zerto_recover_file now returns the resolved flr_path.

Verified end to end against ZVM 10.x: guard tagged cp 1075 on VPG
jp-ubuntu, FLR mounted in ~3s, 158 bytes recovered from the
pre-mutation checkpoint with matching content.

Co-Authored-By: Claude Opus 5 (1M context) <[email protected]>
Claude-Session: https://claude.ai/code/session_016yVfC5nvZowoLFnEGWhLGn

tests/test_recover.py

@@ -28,3 +28,52 @@ def test_flr_list_status():
     ]
     row = flr_row(payload)
     assert flr_status(row).lower() == "mountcompletedsuccessfully"
+
+
+def test_path_items_shapes():
+    from zerto_rewind_mcp.recover import path_items
+
+    assert path_items({"PathItems": [{"Path": "a"}]}) == [{"Path": "a"}]
+    assert path_items([{"Path": "b"}]) == [{"Path": "b"}]
+    assert path_items(None) == []
+
+
+def test_decode_flr_path():
+    from zerto_rewind_mcp.recover import _decode_flr_path
+
+    assert _decode_flr_path("Volume2-Ext4%2fhome%2fjustin%2fapp-config.yaml") == (
+        "Volume2-Ext4/home/justin/app-config.yaml"
+    )
+
+
+def test_resolve_flr_path_picks_browsable_partition():
+    import asyncio
+
+    from zerto_rewind_mcp.recover import resolve_flr_path
+
+    root = {
+        "PathItems": [
+            {"Path": "Volume1-Unknown", "IsBrowsable": False},
+            {"Path": "Volume2-Ext4", "IsBrowsable": True},
+        ]
+    }
+    listing = {
+        "PathItems": [
+            {"Path": "Volume2-Ext4%2fhome%2fjustin%2f.bashrc", "Type": "File"},
+            {"Path": "Volume2-Ext4%2fhome%2fjustin%2fapp-config.yaml", "Type": "File"},
+        ]
+    }
+
+    class FakeClient:
+        def __init__(self):
+            self.seen = []
+
+        async def browse_flr(self, session_id, path="", recursive=False):
+            self.seen.append(path)
+            return root if path == "" else listing
+
+    client = FakeClient()
+    got = asyncio.run(resolve_flr_path(client, "sess", "/home/justin/app-config.yaml"))
+    assert got == "Volume2-Ext4/home/justin/app-config.yaml"
+    # must not try the unrestorable partition
+    assert "Volume1-Unknown/home/justin" not in client.seen