docs: tailor repository documentation to Herbert Ulrich's personal site

[heruberuto]

Motivation

• Replace inherited template documentation with content that reflects this repository as the maintained source for Herbert Ulrich’s personal website (bertik.net) and to ensure content is personal, factual, and not template/demo material.

Description

• Rewrite README.md to describe the project purpose, tech stack, local workflows, content locations, and contribution boundaries specific to Herbert Ulrich.
• Add CONTRIBUTING.md outlining acceptable contributions, items requiring prior discussion, and the local development workflow.
• Add CODE_OF_CONDUCT.md establishing respectful collaboration practices, scope, enforcement, and reporting guidance.
• Update LICENSE to retain upstream attribution and add a copyright line for Herbert Ulrich.

Testing

• Ran pnpm exec prettier --write README.md CONTRIBUTING.md CODE_OF_CONDUCT.md LICENSE which formatted the new/changed docs successfully.
• Verified formatting with pnpm exec prettier --check README.md CONTRIBUTING.md CODE_OF_CONDUCT.md LICENSE, which passed.
• Ran pnpm run lint which completed successfully.
• Running the full repository check pnpm run format:check reported pre-existing formatting issues outside these doc changes in src/components/Header.astro, src/layouts/Layout.astro, and src/scripts/theme.ts (these were not modified by this PR).

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Codex Task