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/blastem.yml

@@ -1,6 +1,7 @@
 emulator: BlastEm
-type: libretro
+type: standalone + libretro
 source: "https://github.com/libretro/blastem"
+upstream: "https://www.retrodev.com/blastem/"
 profiled_date: "2026-03-18"
 core_version: "v0.6.3-pre"
 display_name: "Sega - Mega Drive - Genesis (BlastEm)"
@@ -28,7 +29,28 @@ notes: |
   Sega CD / Mega CD is not supported (only a TODO comment in system.c:16).
   No BIOS files are required or loaded by the libretro core.
 
-files: []
+files:
+  # rom.db is embedded in the libretro binary (libblastem.c:532-540,
+  # extern const char rom_db_data[]). The external file is an optional
+  # override — .info lists it as firmware0_opt=true.
+  # .info sha1 E5414FB1C4CC7D7F5101C07E4547316779BA3D97 does not match
+  # the version in our repo (sha1 02c287d1...) — rom.db changes between
+  # BlastEm releases.
+  - name: rom.db
+    system: sega-megadrive
+    required: false
+    note: "ROM feature database (game-specific mapper/save config). Embedded in core, external is optional override."
+    source_ref: "libblastem.c:532-540 read_bundled_file()"
+
+  # TMSS ROM — only used in standalone mode with tmss-enabled model
+  # libretro build returns NULL for tmss.md (libblastem.c:541)
+  - name: tmss.md
+    system: sega-megadrive
+    required: false
+    mode: standalone
+    size: 2048
+    note: "TMSS startup ROM. Standalone only (models md1va6, md2va1+). Libretro core uses md1va3 (tmss off), no way to change."
+    source_ref: "genesis.c:1910-1923"
 
 analysis:
   tmss: