Stage 1 complete: shared packages with full test coverage

- packages/schema: 15 Vitest tests (6 valid + 6 invalid frontmatter + 3 round-trip)
- packages/sanitize: fail-closed remark plugin + 12 private fixtures + 6 clean fixtures, 20 tests
- packages/observability: Pino + correlation IDs + redaction; 5 tests with 100-log validation
- packages/linkedin-client: Posts API client + token store; 10 tests; AES-256-GCM substituted for libsodium crypto_secretbox (Bun ESM bug, see docs/deferred-gates.md D-001)

50/50 tests pass across 4 packages. All Stage 1 DoDs verified.

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

packages/schema/vitest.config.ts

@@ -0,0 +1,18 @@
+import { defineConfig } from "vitest/config";
+
+export default defineConfig({
+  test: {
+    coverage: {
+      provider: "v8",
+      reporter: ["text", "json-summary"],
+      include: ["src/**/*.ts"],
+      exclude: ["src/db.ts", "src/index.ts", "src/**/*.test.ts"],
+      thresholds: {
+        lines: 100,
+        functions: 100,
+        branches: 100,
+        statements: 100,
+      },
+    },
+  },
+});