Fix memory project persistence through engine serialization

[wbugitlab1]

Summary

• Preserves Memory.project through iii-engine serialization by maintaining an internal memoryProjects sidecar in StateKV.
• Hydrates project fields for memory get and list, while keeping direct row projects authoritative and cleaning sidecar state on delete or explicit project removal.
• Adds regression coverage for the serialization seam, diagnostics, and the previously flaky subprocess watchdog tests.

Closes #303.

Verification

• corepack pnpm exec vitest run test/state-kv-memory-projects.test.ts test/memory-project-engine-serialization.test.ts test/remember-project-scope.test.ts test/diagnostics.test.ts test/infer-memory-projects.test.ts test/context-injection.test.ts test/codex-sdk-provider.test.ts
• corepack pnpm test
• corepack pnpm exec vitest run --coverage --exclude test/integration.test.ts --no-file-parallelism
• corepack pnpm run lint
• corepack pnpm run skills:check
• corepack pnpm run build
• git diff --check origin/main..HEAD
• semgrep scan --config p/default --error --metrics=off .
• gitleaks detect --source . --redact --no-git
• gitleaks detect --source . --redact --log-opts origin/main..HEAD
• gitleaks protect --staged --redact