feat: YAML integration tests with fixtures (35 new, 118 total)

tests/fixtures/ with synthetic platforms, emulators, bios files:
- test_existence.yml: required/optional present/missing
- test_md5.yml: correct/wrong hash, zipped_file (3 cases),
  multi-hash Recalbox, truncated MD5 Batocera, dedup
- test_inherit.yml: YAML inheritance
- _shared.yml: shared groups
- emulator profiles with aliases, standalone mode, alias type

tests/test_integration.py covers:
- existence/md5 mode severity counts
- zipped_file inner ROM verification (3 cases)
- Recalbox multi-hash + Batocera truncated MD5
- worst-status aggregation per destination
- YAML inheritance
- cross-reference: undeclared, standalone skipped, alias skipped
- alias resolution
- pack consistency (verify == pack counts)
- shared groups parsing

All tests use real files, real hashes, real functions, no mocking.

tests/fixtures/emulators/test_emu_alias_only.yml

@@ -0,0 +1,5 @@
+emulator: TestAlias
+type: alias
+alias_of: test_emu_with_aliases
+systems: [test-system]
+files: []

tests/fixtures/emulators/test_emu_with_aliases.yml

@@ -0,0 +1,12 @@
+emulator: TestEmulator
+type: standalone + libretro
+systems: [test-system]
+files:
+  - name: correct_hash.bin
+    required: true
+    aliases: [alt1.bin, alt2.bin]
+  - name: optional_standalone.rom
+    required: false
+    mode: standalone
+  - name: undeclared.bin
+    required: true

tests/fixtures/platforms/_shared.yml

@@ -0,0 +1,7 @@
+shared_groups:
+  test_group:
+    - name: shared_file.bin
+      sha1: "0000000000000000000000000000000000shared"
+      md5: "sharedmd5sharedmd5sharedmd5share"
+      destination: "shared/shared_file.bin"
+      required: false

tests/fixtures/platforms/test_existence.yml

@@ -0,0 +1,22 @@
+platform: TestExistence
+verification_mode: existence
+base_destination: system
+systems:
+  test-system:
+    files:
+    - name: required_present.bin
+      destination: required_present.bin
+      required: true
+      sha1: placeholder
+    - name: required_missing.bin
+      destination: required_missing.bin
+      required: true
+      sha1: "0000000000000000000000000000000000000000"
+    - name: optional_present.bin
+      destination: optional_present.bin
+      required: false
+      sha1: placeholder
+    - name: optional_missing.bin
+      destination: optional_missing.bin
+      required: false
+      sha1: "0000000000000000000000000000000000000001"

tests/fixtures/platforms/test_inherit.yml

@@ -0,0 +1,3 @@
+inherits: test_md5
+platform: TestInherited
+base_destination: BIOS

tests/fixtures/platforms/test_md5.yml

@@ -0,0 +1,58 @@
+platform: TestMD5
+verification_mode: md5
+base_destination: bios
+systems:
+  test-system:
+    files:
+    - name: correct_hash.bin
+      destination: correct_hash.bin
+      required: true
+      md5: placeholder
+    - name: wrong_hash.bin
+      destination: wrong_hash.bin
+      required: true
+      md5: "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa"
+    - name: no_md5_present.bin
+      destination: no_md5_present.bin
+      required: true
+    - name: required_missing.bin
+      destination: required_missing.bin
+      required: true
+      md5: "bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb"
+    - name: optional_missing.bin
+      destination: optional_missing.bin
+      required: false
+      md5: "cccccccccccccccccccccccccccccccc"
+  test-zip-system:
+    files:
+    - name: test.zip
+      destination: test.zip
+      required: true
+      md5: placeholder_zip_md5
+      zipped_file: inner.rom
+    - name: test_bad.zip
+      destination: test_bad.zip
+      required: true
+      md5: placeholder_bad_zip_md5
+      zipped_file: inner.rom
+    - name: test_missing_inner.zip
+      destination: test_missing_inner.zip
+      required: true
+      md5: placeholder_missing_inner_md5
+      zipped_file: not_there.rom
+  test-recalbox-system:
+    files:
+    - name: multi_hash.bin
+      destination: multi_hash.bin
+      required: true
+      md5: placeholder_multi
+    - name: truncated_md5.bin
+      destination: truncated_md5.bin
+      required: true
+      md5: placeholder_truncated
+  test-dedup-system:
+    files:
+    - name: correct_hash.bin
+      destination: correct_hash.bin
+      required: true
+      md5: "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa"