feat: add prompt, root, emptyOutDir options and CI workflow

[koistya]

Summary

• Add prompt bundle option to prepend instructions or content to bundles
• Add root config option for specifying custom project root
• Add emptyOutDir option with smart defaults based on outDir location
• Add exclude option to skip specific bundles during upload
• Add GitHub Actions CI workflow for automated testing
• Fix gitignore negation pattern support
• Add Product Hunt badge to docs site

New Features

Prompt Option

Prepend instructions or file content to bundles:

export default defineConfig({
  bundles: {
    review: {
      include: "src/**/*",
      prompt: "./prompts/review.md",  // load from file
    },
    analyze: {
      include: "lib/**/*",
      prompt: "Analyze this code for performance issues.",  // inline
    },
  },
});

Root Option

Bundle from a subdirectory:

export default defineConfig({
  root: "./packages/app",
  bundles: {
    app: "src/**/*",  // matches packages/app/src/**/*
  },
});

emptyOutDir Option

Control output directory cleaning:

npx srcpack --emptyOutDir      # always empty
npx srcpack --no-emptyOutDir   # never empty

Auto-enabled when outDir is inside project root; shows warning otherwise.

Upload Exclude

Skip bundles from upload:

upload: {
  provider: "gdrive",
  clientId: "...",
  clientSecret: "...",
  exclude: ["local", "debug"],
}

Test Plan

• Unit tests for prompt option (inline, file-based, empty handling)
• Unit tests for root path resolution (relative, absolute, tilde)
• Unit tests for emptyOutDir behavior
• Unit tests for upload exclude option
• Test gitignore negation patterns with new fixture
• CI workflow runs on PR