refactor: reorganize data/processed/ into mcgill/ and user/ subdirs

Moved data/processed/{train,val,holdout}/ → data/processed/mcgill/{train,val,holdout}/
so both corpora have their own namespace under data/processed/.
Updated PRETRAIN_DATA paths in make_colab_zip.py accordingly
(path remap workaround no longer needed).

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

scripts/make_colab_zip.py

@@ -4,8 +4,8 @@ pretrain mode (default):
   - src/                               (all Python modules)
   - scripts/pretrain.py
   - requirements.txt
-  - data/processed/mcgill/train/*.pt   (remapped from data/processed/train/)
-  - data/processed/mcgill/val/*.pt     (remapped from data/processed/val/)
+  - data/processed/mcgill/train/*.pt
+  - data/processed/mcgill/val/*.pt
 
 finetune mode:
   - src/                               (all Python modules)
@@ -57,8 +57,8 @@ MODE_SCRIPTS: dict[str, list[str]] = {
 
 # Local dir → arc path inside zip
 PRETRAIN_DATA: list[tuple[Path, str]] = [
-    (ROOT / "data" / "processed" / "train", "data/processed/mcgill/train"),
-    (ROOT / "data" / "processed" / "val",   "data/processed/mcgill/val"),
+    (ROOT / "data" / "processed" / "mcgill" / "train", "data/processed/mcgill/train"),
+    (ROOT / "data" / "processed" / "mcgill" / "val",   "data/processed/mcgill/val"),
 ]
 
 FINETUNE_DATA: list[tuple[Path, str]] = [