Re-enable Stripe billing (currently pinned for early access)

[rogadev]

Billing is fully implemented but dormant: with no Stripe env vars set, billingEnabled() is false, the app runs unlocked with password-only accounts, and all billing UI (nav item, trial banner, signup/landing trial copy) is hidden. See commit 69c18f1.

Why it's pinned

Ryan couldn't get access to the Stripe account when we tried to authorize the Stripe MCP plugin (June 11, 2026). Everything code-side is done and merged — this is purely account/config work.

To re-enable

1. Stripe account access — resolve login issues (this was the blocker).
2. Create the product/price — "EzEval", recurring $5.00 USD/month → copy the price ID. (The Stripe MCP plugin can do this once authorized.)
3. Webhook endpoint — https://ezeval.app/api/stripe/webhook, events: checkout.session.completed, customer.subscription.created, customer.subscription.updated, customer.subscription.deleted → copy the signing secret.
4. Set env vars (locally in .env and in the Vercel project):
   • STRIPE_SECRET_KEY
   • STRIPE_PRICE_ID
   • STRIPE_WEBHOOK_SECRET
5. Revisit early-access copy — landing page and signup currently say "free during early access · $5/month at launch"; restore trial/subscribe wording when billing goes live (src/routes/+page.svelte, src/routes/signup/+page.svelte).
6. Decide grandfathering — businesses created during early access have a trialEndsAt 14 days after signup, which will likely be in the past when billing turns on; they'll be locked to the billing page on their next visit. Either extend trial_ends_at for existing rows or let them subscribe immediately.
7. Test the flow — checkout with test cards (4242 4242 4242 4242), webhook delivery, past-due banner, lock/unlock gating.

Setting the three env vars is the only switch — no code changes needed to turn billing back on.

[rogadev]

Added in 6a23de4: owner signups now land on /app/welcome while billing is pinned — a founding-member congrats page ("limited-time free membership, we'll ask for payment details later"). It auto-redirects to /app once Stripe env vars are set.

When re-enabling billing, also:

• Replace this welcome step with the real onboarding flow: short free trial but collect the card up front at signup (Stripe Checkout in subscription mode with trial_period_days, or SetupIntent + subscription with trial).
• Signup redirect logic lives in src/routes/signup/+page.server.ts (billingEnabled() ? '/app' : '/app/welcome').
• The welcome page itself (src/routes/app/welcome/) can be deleted or repurposed at that point.
• Remember the founding-member promise: existing early-access businesses were told they'd get notice before payment is required — handle their transition gracefully (ties into the grandfathering item above).