v2: release versions and integrations

Spec: SPEC. Build log: PROGRESS. Merged in PR #13. The AIDE logo source is in docs/v2/brand.

• Release versions. Each release has a semver version with internal checkpoints. Rollback is limited to the version in development, and a released version is closed.
• Import an existing repo. A Repository Analyst writes a codebase summary first.
• Repo tools for agents. Read-only list_files, read_file and search_code on a credential-free snapshot.
• Tech stack presets. Retired in v4.
• GitHub App. Registered through the manifest flow. Background Git work uses short-lived installation tokens.
• Per-user LLM connections, merge strategies, check runs as review input and GitHub Releases.
• Vercel deployments. Preview in review, production on release, with promote and redeploy.
• A new UI shell with one page per lifecycle stage.