fix: match mod folder by steam_id when folder name diverges from modlist name

_find_folder in mods.py now has a fourth fallback: reads publishedid from
meta.cpp inside each candidate folder and matches against mod["steam_id"].
Fixes mods appearing as "not downloaded" when the folder name on disk differs
from the name in the modlist but the mod content (meta.cpp) is correct.

Also adds 8 tests covering all four match strategies and edge cases.

gui/views/mods.py

@@ -7,7 +7,7 @@ from typing import TYPE_CHECKING, Optional
 
 import customtkinter as ctk
 
-from arma_modlist_tools.fetcher import _normalize_name
+from arma_modlist_tools.fetcher import _normalize_name, _parse_meta_cpp
 from gui._constants import COLOR_OK, COLOR_ERROR, COLOR_WARN, COLOR_RUNNING
 from gui.locales import t
 from gui.views.base import BaseView
@@ -16,13 +16,14 @@ if TYPE_CHECKING:
     from gui.app import ArmaModManagerApp
 
 
-def _find_folder(group_dir: Path, mod_name: str) -> Optional[Path]:
+def _find_folder(group_dir: Path, mod_name: str, steam_id: str | None = None) -> Optional[Path]:
     """Return the local mod folder path, or None if not downloaded.
 
     Matches in priority order:
     1. Exact folder name ``@{mod_name}``
     2. Case-insensitive name (handles ``@CBA_A3`` vs ``CBA_A3``)
     3. Normalized name — strips non-alphanumeric (handles ``@cba_a3`` vs ``CBA A3``)
+    4. Steam ID match via ``meta.cpp`` ``publishedid`` field (folder name differs from modlist name)
     """
     if not group_dir.is_dir():
         return None
@@ -38,6 +39,18 @@ def _find_folder(group_dir: Path, mod_name: str) -> Optional[Path]:
             return p
         if _normalize_name(p.name) == target_norm:
             return p
+    # Fallback: match by steam_id via meta.cpp when folder name diverges from modlist name
+    if steam_id:
+        for p in group_dir.iterdir():
+            if not p.is_dir():
+                continue
+            meta = p / "meta.cpp"
+            try:
+                sid = _parse_meta_cpp(meta.read_text(encoding="utf-8", errors="replace"))
+                if sid == steam_id:
+                    return p
+            except OSError:
+                pass
     return None
 
 
@@ -215,7 +228,7 @@ class ModsView(BaseView):
         link_map: dict[str, bool],
     ) -> None:
         for i, mod in enumerate(sorted(mods, key=lambda m: m["name"].lower())):
-            folder_path = _find_folder(cfg.downloads / group, mod["name"])
+            folder_path = _find_folder(cfg.downloads / group, mod["name"], mod.get("steam_id"))
             downloaded  = folder_path is not None
             linked      = (link_map.get(folder_path.name.lower(), False)
                            if folder_path else False)