feat: agnostic bios mode for filename-agnostic emulators

bios_mode: agnostic (profile) and agnostic: true (file) for
emulators that accept any valid BIOS without specific filename.
find_undeclared_files skips agnostic entries, pack extras scan
includes all matching DB files by path prefix + size criteria,
resolve_local_file has agnostic fallback with rename README.
applied to pcsx2, lrps2 (bios_mode), melonds dsi_nand (file).

emulators/lrps2.yml

@@ -5,6 +5,7 @@
 emulator: LRPS2
 type: libretro
 core_classification: community_fork
+bios_mode: agnostic
 source: "https://github.com/libretro/ps2"
 upstream: "https://github.com/PCSX2/pcsx2"
 profiled_date: "2026-03-25"

emulators/melonds.yml

@@ -77,6 +77,7 @@ files:
     source_ref: "src/SPI.cpp:197-211, src/frontend/Util_ROM.cpp:201-217"
 
   - name: dsi_nand.bin
+    agnostic: true
     system: nintendo-dsi
     description: "DSi NAND dump"
     required: true

emulators/pcsx2.yml

@@ -1,6 +1,7 @@
 emulator: PCSX2
 type: standalone
 core_classification: official_port
+bios_mode: agnostic
 source: "https://github.com/PCSX2/pcsx2"
 upstream: "https://github.com/PCSX2/pcsx2"
 cores: