feat: add support for devcontainer

[LukeSeers]

Description

Add support for a preconfigured Devcontainer so contributors get an identical, ready-to-run development environment without manual Node/Cloudflare setup. The devcontainer builds on Node LTS, pre-installs dependencies onto Docker volumes, and hardens the husky pre-commit hook so host-side commits degrade gracefully when npm/node_modules aren't available.

I've only tested this with JetBrains

Changes

• Add .devcontainer/Dockerfile, devcontainer.json, and setup.sh bootstrap (Node LTS image, sudo for node user, forwards port 9115, mounts node_modules on Docker volumes, WebStorm backend configured)
• Update .husky/pre-commit to resolve npm from container-typical paths and skip lint/type-check with a clear warning when running outside the container (CI still enforces on push)
• Update README contributing section to document the Devcontainer workflow (npm install, npm run build:core, npm run db:reset, npm run dev → http://localhost:9115)

Testing

• Setup is exercised locally via Docker devcontainer bring-up; postCreateCommand runs an idempotent npm install with retry logic for transient bind-mount EACCES/EPERM failures on Docker Desktop + WSL2
• Pre-commit hook tested to skip cleanly from a host where npm/node_modules are not visible

Unit Tests

• Added/updated unit tests
• All unit tests passing (no runtime code changes; hook behavior is environment-based)

E2E Tests

• Added/updated E2E tests
• All E2E tests passing

Checklist

• Code follows project conventions
• Tests added/updated and passing
• Type checking passes
• No console errors or warnings
• Documentation updated (if needed)