feat: add load_from field for non-system_dir files

Replaces mode: standalone hack with load_from: save_dir on Panda3DS
files. The load_from field documents which libretro directory callback
provides the base path (system_dir default, save_dir, content_dir).
Pack generator and cross-reference skip files not targeting system_dir.

emulators/panda3ds.yml

@@ -24,7 +24,7 @@ notes: |
 files:
   - name: "aes_keys.txt"
     path: "Emulator Files/sysdata/aes_keys.txt"
-    mode: standalone
+    load_from: save_dir
     description: "AES encryption keys for decrypting encrypted ROMs"
     required: false
     source_ref: "src/emulator.cpp:229,237-238, src/core/crypto/aes_engine.cpp:13-92"
@@ -37,7 +37,7 @@ files:
 
   - name: "seeddb.bin"
     path: "Emulator Files/sysdata/seeddb.bin"
-    mode: standalone
+    load_from: save_dir
     description: "Seed database for seed-encrypted games"
     required: false
     source_ref: "src/emulator.cpp:230,241-242, src/core/loader/ncch.cpp:78-93"

scripts/generate_pack.py

@@ -402,6 +402,10 @@ def _collect_emulator_extras(
                 continue
             if file_mode == "libretro" and is_standalone:
                 continue
+            # Skip files loaded from non-system directories (save_dir, content_dir)
+            load_from = f.get("load_from", "")
+            if load_from and load_from != "system_dir":
+                continue
             if is_standalone:
                 dest = f.get("standalone_path") or f.get("path") or fname
             else:

scripts/verify.py

@@ -327,6 +327,10 @@ def find_undeclared_files(
                 continue
             if file_mode == "libretro" and is_standalone:
                 continue
+            # Skip files loaded from non-system directories (save_dir, content_dir)
+            load_from = f.get("load_from", "")
+            if load_from and load_from != "system_dir":
+                continue
 
             archive = f.get("archive")