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>

src/mcp_synology_filestation/tools/filestation.py

@@ -154,6 +154,7 @@ def register_filestation(
                     "limit": limit,
                     "sort_by": sort_by,
                     "sort_direction": sort_direction,
+                    "additional": json.dumps(["size", "time"]),
                 },
             )
         except SynologyError as e:
@@ -165,22 +166,43 @@ def register_filestation(
         if not files:
             return f"Directory '{path}' is empty (or does not exist)."
 
-        # Build table — name + type only (no additional fields requested)
+        # Build table
         rows = []
         for f in files:
             name = f.get("name", "")
-            ftype = "dir" if f.get("isdir", False) else "file"
-            rows.append((name, ftype))
+            is_dir = f.get("isdir", False)
+            ftype = "dir" if is_dir else "file"
+            add = f.get("additional", {})
+            size_str = "-" if is_dir else _fmt_size(add.get("size"))
+            mtime_str = _fmt_time(add.get("time", {}).get("mtime"))
+            rows.append((name, ftype, size_str, mtime_str))
 
         w_name = max(len("Name"), *(len(r[0]) for r in rows))
         w_type = max(len("Type"), *(len(r[1]) for r in rows))
+        w_size = max(len("Size"), *(len(r[2]) for r in rows))
+        w_mtime = max(len("Modified"), *(len(r[3]) for r in rows))
 
-        sep = f"+{'-' * (w_name + 2)}+{'-' * (w_type + 2)}+"
-        header = f"| {'Name':<{w_name}} | {'Type':<{w_type}} |"
+        sep = (
+            f"+{'-' * (w_name + 2)}"
+            f"+{'-' * (w_type + 2)}"
+            f"+{'-' * (w_size + 2)}"
+            f"+{'-' * (w_mtime + 2)}+"
+        )
+        header = (
+            f"| {'Name':<{w_name}} "
+            f"| {'Type':<{w_type}} "
+            f"| {'Size':<{w_size}} "
+            f"| {'Modified':<{w_mtime}} |"
+        )
 
         lines = [f"Path: {path}", sep, header, sep]
-        for name, ftype in rows:
-            lines.append(f"| {name:<{w_name}} | {ftype:<{w_type}} |")
+        for name, ftype, size_str, mtime_str in rows:
+            lines.append(
+                f"| {name:<{w_name}} "
+                f"| {ftype:<{w_type}} "
+                f"| {size_str:<{w_size}} "
+                f"| {mtime_str:<{w_mtime}} |"
+            )
         lines.append(sep)
 
         end = offset + len(files)