feat(scripts): add library-decisions trace schema + template

Creates the shared schema module for library evaluation traces
(ADR-022 §4): Zod-validated frontmatter with all 8 filter fields and
enum constraints, plus parseTrace/validateTrace exports and a custom
YAML frontmatter parser for the nested trace format.

Also adds docs/library-decisions/_template.md with all 11 required
headings (8 Filter + 3 Prompt) in machine-checkable ADR-022 order.

Adds zod as a root devDependency so the script is runnable directly
from the workspace root without a package context.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

package.json

@@ -28,6 +28,7 @@
   },
   "devDependencies": {
     "@ai-hero/sandcastle": "*",
+    "zod": "^3.25.0",
     "@playwright/test": "^1.49.0",
     "@stryker-mutator/core": "^8.7.0",
     "@stryker-mutator/vitest-runner": "^8.7.0",