test(snapshot): Add JSON fixture schema validation

Add a dedicated schema corpus for structured JSON fixtures and validate
each discovered fixture against its declared schema and version.

This gives the hand-crafted fixture contracts an executable check
without coupling them to the existing text snapshot harness.

Co-Authored-By: OpenAI Codex <noreply@openai.com>

Author: cameroncooke

package-lock.json

@@ -46,6 +46,7 @@
     "license:check": "npx -y license-checker --production --onlyAllow 'MIT;ISC;BSD-2-Clause;BSD-3-Clause;Apache-2.0;Unlicense;FSL-1.1-MIT'",
     "knip": "knip",
     "test": "vitest run",
+    "test:schema-fixtures": "vitest run --config vitest.snapshot.config.ts src/snapshot-tests/__tests__/json-fixture-schema.test.ts",
     "test:snapshot": "npm run build && node build/cli.js daemon stop 2>/dev/null; vitest run --config vitest.snapshot.config.ts",
     "test:snapshot:update": "npm run build && node build/cli.js daemon stop 2>/dev/null; UPDATE_SNAPSHOTS=1 vitest run --config vitest.snapshot.config.ts",
     "test:smoke": "npm run build && vitest run --config vitest.smoke.config.ts",
@@ -99,6 +100,7 @@
     "@types/yargs": "^17.0.33",
     "@vitest/coverage-v8": "^3.2.4",
     "@vitest/ui": "^3.2.4",
+    "ajv": "^8.18.0",
     "eslint": "^9.23.0",
     "eslint-config-prettier": "^10.1.1",
     "eslint-plugin-prettier": "^5.2.5",