Three pieces of authentication work that need to land together so OAuth
sign-ins produce a usable session.
* `ensureUserIdByEmail` upserts a `users` row on every OAuth sign-in
matched case-insensitively on email, then stamps `token.id` with the
resulting UUID so workspace-scoped tRPC procedures can resolve
membership. Credentials sign-in already returned the DB id from
`authorize`; OAuth now does the equivalent.
* `ensureUserHasWorkspace` mints a personal workspace (and `owner`
member row) on first sign-in for any user that doesn't already
belong to one, so fresh OAuth accounts don't land in the app with
no tenant scope. Idempotent; slug collisions retry with a random
suffix and cap at 5 attempts.
* Migration 0004 adds a `UNIQUE (lower(email))` index on `users` to
match the lookup pattern and prevent two providers from minting
rows that differ only in casing. Existing rows are normalized to
lowercase first; the column-level UNIQUE catches any pre-existing
duplicates so they get resolved by a human rather than silently
merged.
Sign-in / sign-up pages add an Authentik SSO button (gated on
`AUTH_AUTHENTIK_*` env vars). Layout switches to GitHub+Google on top
with Authentik full-width below.
Co-authored-by: Cursor <cursoragent@cursor.com>
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