Phase 0: Set up npm workspaces and TypeScript configs

[ericmmartin]

Goal

Stand up the monorepo skeleton so subsequent Phase 0 issues have a place to land code.

Acceptance criteria

• Root package.json with npm workspaces declaring packages/*
• packages/plugin/package.json (no deps yet beyond what the spike needs)
• packages/orchestrator/package.json (stub; populated in Phase 2)
• packages/shared/package.json (stub; populated in Phase 2)
• tsconfig.base.json at the root with shared strict-mode settings
• Per-package tsconfig.json extending the base
• pnpm-workspace.yaml or equivalent (whatever package manager we settle on)

Notes

The plugin (Phase 0–1) is pure bash and doesn't actually need TypeScript yet. The TS setup is forward-looking for the orchestrator (Phase 2) and the shared types package. Setting it up now means Phase 2 work doesn't get derailed by infra.

Out of scope

• Drizzle schema (Phase 2)
• Actual TS source files (Phase 1+)

semver: minor