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.

CLAUDE.md

@@ -101,10 +101,11 @@ Pass 2 builds `ok_disk_names` — the set of disk names that already match the s
 - `logs.py` — real-time log viewer fed from the stdout/stderr queue
 - `settings.py` — in-app editor for `config.json` (server URL, paths, credentials)
 
-**`_find_folder` (mods.py) — three-level name matching:** The mods view resolves a mod's local folder by mod name from `comparison.json`, which may differ from the server-canonical folder name used by the fetcher. Lookup order:
+**`_find_folder` (mods.py) — four-level name matching:** The mods view resolves a mod's local folder by mod name from `comparison.json`, which may differ from the server-canonical folder name used by the fetcher. Lookup order:
 1. Exact: `@{mod_name}`
 2. Case-insensitive: `@CBA_A3` matches `CBA_A3`
 3. Normalized (`_normalize_name`): strips all non-alphanumeric — handles punctuation/spacing differences, e.g. `@US GEAr- Units (IFA3)` matches `US GEAr: Units (IFA3)` (both → `usgearunitsifa3`)
+4. Steam ID via `meta.cpp`: reads `publishedid` from each folder's `meta.cpp` and matches against `mod["steam_id"]` — handles the case where the folder name bears no resemblance to the modlist name but the mod content is correct
 
 **`selection.json`** — GUI selection state file, tracked in git. Persists which mods/groups are selected between GUI sessions. Written by the GUI; safe to delete (GUI recreates it on next save).