Slice 3 — User can create an empty Repository and 'git clone' it over HTTPS

[safayavatsal]

What to build

End-to-end repository creation and HTTPS clone. This is the first slice where GitRepository (the deep module) earns its keep.

• Web UI: "New Repository" form with name and (deferred-elsewhere) visibility flag. Repository list page on the user's profile.
• platform-api: POST /repos, GET /repos, GET /repos/:owner/:name endpoints. On create, GitRepository.Init runs and produces a bare repo on EBS.
• HTTPS Git transport: platform-api mounts git-http-backend (or equivalent) at /:owner/:name.git/.... An empty repo can be cloned with git clone https://forge.../<owner>/<name>.git.
• Auth on Git HTTPS: at this slice, accept the session cookie from web. Personal Access Tokens come in slice 12.

Acceptance criteria

• A signed-in user can create a Repository named hello-world from the web UI.
• The Repository appears in the user's repo list.
• git clone https://forge.../<owner>/hello-world.git against an empty Repository succeeds and produces a valid empty Git working tree.
• Cloning a non-existent repository returns a clean 404 without leaking internal errors.
• GitRepository has unit tests covering Init, ListRefs on an empty repo, and idempotent re-init protection.
• Repository slugs are validated (lowercase, alphanumeric + dash, length limits).

Blocked by

• Slice 2 — OAuth login (GitHub + Google) end-to-end via SuperTokens #2