feat: core profiles, data_dirs buildbot, cross_ref fix

profiles: amiberry (new), amiarcadia, atari800, azahar, b2,
bk, blastem, bluemsx, freeintv updated with source refs,
upstream field, mode field, data_directories.

_data_dirs.yml: buildbot source for retroarch platforms,
strip_components for nested ZIPs, freeintv-overlays fixed.

cross_reference.py: data_directories-aware gap analysis,
suppresses false gaps when emulator+platform share refs.

refresh_data_dirs.py: ZIP strip_components support,
for_platforms filter, ETag freshness for buildbot.

scraper: bluemsx single ref, freeintv overlays injection.
generate_pack.py: warning on missing data directory cache.

emulators/bluemsx.yml

@@ -1,6 +1,7 @@
 emulator: blueMSX
-type: libretro
+type: standalone + libretro
 source: "https://github.com/libretro/blueMSX-libretro"
+upstream: "http://bluemsx.msxblue.com/"
 profiled_date: "2026-03-18"
 core_version: "SVN"
 display_name: "MSX/SVI/ColecoVision/SG-1000 (blueMSX)"
@@ -52,6 +53,13 @@ notes: |
   C-BIOS machines work for cartridge-based games without any copyrighted BIOS.
   For disk/tape support, real BIOS ROMs are required.
 
+data_directories:
+  # 302 files: 296 in Machines/ (200 machine configs + ROMs) + 6 in Databases/
+  # buildbot source: https://buildbot.libretro.com/assets/system/blueMSX.zip
+  # ref: libretro.c:1118-1119 — system_dir/Machines/ + system_dir/Databases/
+  - ref: bluemsx
+    source_ref: "libretro.c:1118-1119"
+
 files:
   # ============================================================
   # Shared ROMs (Machines/Shared Roms/)