feat(skill-tests): negative cases for platform-dependent skills

Add expectError test cases for db-create, db-load-xml, db-dump-xml,
db-dump-cf, db-load-cf, db-update, db-run, epf-build, epf-dump.
Tests parameter validation (missing args, bad file paths, partial
mode without required params). Total: 301 cases.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

tests/skills/cases/db-dump-xml/_skill.json

@@ -0,0 +1,9 @@
+{
+  "script": "db-dump-xml/scripts/db-dump-xml",
+  "setup": "none",
+  "args": [],
+  "snapshot": {
+    "root": "workDir",
+    "normalizeUuids": false
+  }
+}