fix: restore additional=["size","time"] to list_dir, update SPEC + tests

Root cause of DSM 408 was wrong path format (volume path vs share path),
not the additional parameter. Confirmed via test_additional.py that
json.dumps(["size","time"]) is the correct format; comma-separated string
is silently ignored by DSM.

- list_dir: restore 4-column table (Name, Type, Size, Modified)
- list_dir: use additional=json.dumps(["size","time"]) (confirmed working)
- SPEC.md: document share path requirement, additional format rules,
  note SYNO.FileStation.Stat unavailability, remove comma-sep gotcha
- tests: restore size/mtime mock data and assertions
- delete test_additional.py (throwaway diagnostic script)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

tests/test_tools_filestation.py

@@ -79,7 +79,7 @@ async def test_list_shares_success(config: AppConfig) -> None:
     result = await tools["list_shares"]()
 
     assert "data" in result
-    assert "/data" in result          # share path, not volume path
+    assert "/data" in result  # share path, not volume path
     assert "/volume1/data" not in result
     assert "photos" in result
     assert "2 share(s) found" in result
@@ -121,15 +121,27 @@ async def test_list_shares_dsm_error(config: AppConfig) -> None:
 
 @pytest.mark.asyncio
 async def test_list_dir_success(config: AppConfig) -> None:
-    """list_dir returns a formatted table with name and type columns."""
+    """list_dir returns a formatted table with name, type, size, and modified columns."""
     client = MagicMock()
     client.request = AsyncMock(
         return_value={
             "total": 3,
             "files": [
-                {"name": "documents", "isdir": True},
-                {"name": "photo.jpg", "isdir": False},
-                {"name": "readme.txt", "isdir": False},
+                {
+                    "name": "documents",
+                    "isdir": True,
+                    "additional": {"size": 0, "time": {"mtime": 1700000000}},
+                },
+                {
+                    "name": "photo.jpg",
+                    "isdir": False,
+                    "additional": {"size": 2_048_000, "time": {"mtime": 1710000000}},
+                },
+                {
+                    "name": "readme.txt",
+                    "isdir": False,
+                    "additional": {"size": 512, "time": {"mtime": 1720000000}},
+                },
             ],
         }
     )
@@ -142,6 +154,11 @@ async def test_list_dir_success(config: AppConfig) -> None:
     assert "readme.txt" in result
     assert "dir" in result
     assert "file" in result
+    # Size column: dirs show "-", files show human-readable size
+    assert "2 MB" in result or "1 MB" in result  # photo.jpg ~2 MB
+    assert "512 B" in result  # readme.txt
+    # Modified column present
+    assert "Modified" in result
     assert "Showing 1–3 of 3 item(s)" in result
 
 
@@ -153,7 +170,11 @@ async def test_list_dir_pagination(config: AppConfig) -> None:
         return_value={
             "total": 200,
             "files": [
-                {"name": f"file{i}.txt", "isdir": False}
+                {
+                    "name": f"file{i}.txt",
+                    "isdir": False,
+                    "additional": {"size": 100, "time": {"mtime": 1700000000}},
+                }
                 for i in range(100)
             ],
         }