Add reproducible JSON server configs, Zod validator, and admin JSON import UI

[Spbd1]

Motivation

• Provide reproducible, shareable server configurations for experiments so servers can be created deterministically from a single JSON artifact.
• Validate and convert those configs into engine overrides to avoid ad-hoc manual changes and ensure engine behavior matches published configs.
• Make it easy for admins to paste/upload and validate configs in the admin UI before creating a server to reduce setup errors.

Description

• Added five reproducible JSON configs under configs/: lowineq-stable.json, lowineq-uncertain.json, highineq-stable.json, highineq-uncertain.json, and pilot-8servers.json, each containing the requested top-level fields, defaults and a randomSeed.
• Introduced a shared Zod-based schema and helpers at packages/shared/src/serverConfig.ts to parse/validate configs and map them to engine override keys via serverConfigToEngineOverrides.
• Exported the config helpers from @parcel-society/shared (packages/shared/src/index.ts) and added zod to packages/shared/package.json dependencies.
• Added a client-side admin form apps/web/app/admin/servers/new/ConfigJsonForm.tsx to paste or upload JSON, run local validation via safeParseServerConfig, show validation messages, and enable create actions only when valid; wired the form into the admin create-server page and added createServerFromConfig server action to persist the server and optionally generate the configured map (apps/web/app/admin/servers/new/actions.ts, apps/web/app/admin/servers/new/page.tsx).

Testing

• Ran a Python structural check that parsed all files in configs/ and asserted the expected keys and default values, which passed.
• Ran git diff --check / local whitespace checks, which passed.
• Attempted pnpm --filter @parcel-society/shared typecheck && pnpm --filter @parcel-society/web typecheck, but TypeScript checks could not complete because node_modules are missing and the package install is blocked by registry access (TypeScript errors due to unresolved zod).
• Attempted pnpm --filter @parcel-society/web lint, but ESLint could not run because dependencies are unavailable and @eslint/js could not be resolved.

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Codex Task