add ci and release workflows

[draylegend]

Context

Split out of #3 — electrobun itself now builds correctly (dev + stable), but there's no CI validating it on push/PR, and no automated release pipeline publishing to GitHub Releases.

What's needed

• CI workflow: on push/PR to dev, run nx run-many -t lint test build + nx build desktop --configuration=dev on windows-latest (using oven-sh/setup-bun)
• Release workflow: on v* tag push, run nx build desktop (stable) and publish artifacts/* to a GitHub Release via softprops/action-gh-release
• release.baseUrl in electrobun.config.ts should point at https://github.com/draylegend/letora/releases/latest/download for auto-update to work off GitHub Releases

Draft workflow YAML (written and locally verified against this repo's nx build desktop targets, not yet committed):

.github/workflows/ci.yml:

name: CI

on:
  push:
    branches: [dev]
  pull_request:
    branches: [dev]

jobs:
  build:
    runs-on: windows-latest
    steps:
      - uses: actions/checkout@v4
      - uses: oven-sh/setup-bun@v2
        with:
          bun-version: latest
      - run: bun install --frozen-lockfile
      - run: bunx nx run-many -t lint test build
      - run: bunx nx build desktop --configuration=dev

.github/workflows/release.yml:

name: Release

on:
  push:
    tags: ['v*']

permissions:
  contents: write

jobs:
  release:
    runs-on: windows-latest
    steps:
      - uses: actions/checkout@v4
      - uses: oven-sh/setup-bun@v2
        with:
          bun-version: latest
      - run: bun install --frozen-lockfile
      - run: bun run build:stable
      - uses: softprops/action-gh-release@v2
        with:
          files: artifacts/*
          generate_release_notes: true

Both were run locally against this repo (after #3's apps/desktop Nx project) and produced correct output.