docs(community): improve contributor onboarding

[flotob]

Summary

• add contributor guidance covering issue scope, architecture, verification, MPL-2.0 licensing, and accountable AI assistance
• replace the 776-line README with a concise project landing page and move detailed feature, protocol, configuration, development, and troubleshooting material under docs/
• add structured bug and feature issue forms plus a lightweight pull request template
• align local development, CI, and package engines on Node.js 24 LTS; repair the existing npm 11 lockfile gap for optional Electron Windows-signing packages
• refresh the live repository description and homepage metadata

Impact

New contributors get one supported setup path, clear contribution expectations, structured reporting fields tailored to Freedom's protocols and node modes, and navigable documentation without losing the technical material previously embedded in the README.

Verification

• npm ci on Node.js 24.18.1 / npm 11.16.0
• npm run lint
• npm test — 145 suites passed, 2,838 tests passed, 10 skipped
• Prettier check for all changed Markdown, YAML, JSON, and workflow files
• YAML parse validation for both issue forms, their chooser config, and CI
• local-link validation for all changed Markdown files
• git diff --check
• staged secret-pattern scan

The repository-wide npm run format:check still reports pre-existing formatting drift and parser failures in untouched files, notably src/renderer/pages/settings.html and src/renderer/vendor/qrcode.min.js; every file changed here passes Prettier.

Closes #183
Closes #184
Closes #185