feat: self-serve developer access for paid tiers, split BYOK into its own permission (v0.72.0)

Splits what was one isDeveloper flag (gating webhooks, API keys, AND
BYOK together) into two independent permissions:

- isDeveloper (webhooks + self-serve API keys): admin-toggled as
  before, but now ALSO self-serve -- PATCH /api/v1/users/me/developer-access
  lets any paid-tier (tier !== "free") user turn it on themselves, no
  added fee. Free tier still needs an admin grant. Turning it off is
  always self-serve regardless of tier, since revoking your own
  access needs no gatekeeping. canSelfServeDeveloperAccess() in
  lib/permissions.ts is the single check for "is this tier eligible."

- isByokEnabled (BYOK AI provider keys): new column, admin-only, no
  self-serve path at all -- routing real AI provider spend through
  Epicure on the user's own key warrants a manual admin check-in that
  webhooks/API access don't need. requireByok() replaces
  requireDeveloper() on the three ai-keys routes.

Migration adds is_byok_enabled and grandfathers in anyone who already
has a BYOK key configured (the earlier grandfather migration only
covered the combined isDeveloper flag, which BYOK no longer reads).

Settings UI: webhooks/API-keys pages show a self-serve "Enable"
toggle for paid-tier non-developers instead of the locked notice
(still shown to free-tier users), plus a "Disable developer access"
link once enabled. Settings -> AI's BYOK section now checks
isByokEnabled instead of isDeveloper -- unaffected by the self-serve
change, still fully admin-gated.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

apps/web/lib/permissions.ts

@@ -1,8 +1,22 @@
-/** Gates webhooks, self-serve API keys, and BYOK AI provider keys.
- * Admin-granted only for now (users.isDeveloper, toggled in
- * admin/users/[id]) — kept as a single function so a future
- * subscription-based auto-grant (e.g. `|| tier !== "free"`) is a one-line
- * change here, not a redesign across every call site. */
+/** Gates webhooks and self-serve API keys. Admin-settable always
+ * (users.isDeveloper, toggled in admin/users/[id]); also self-serve
+ * toggleable by the user themselves once on a paid tier, no added fee —
+ * see PATCH /api/v1/users/me/developer-access. Both paths write the same
+ * column, so this check doesn't need to know which one granted it. */
 export function hasDeveloperAccess(user: { isDeveloper: boolean }): boolean {
   return user.isDeveloper;
 }
+
+/** Gates BYOK AI provider keys — deliberately separate from
+ * hasDeveloperAccess: routing real AI provider spend through Epicure on
+ * the user's own key warrants a manual admin check-in, not blanket
+ * self-serve like webhooks/API keys get. Admin-only, no self-serve path. */
+export function hasByokAccess(user: { isByokEnabled: boolean }): boolean {
+  return user.isByokEnabled;
+}
+
+/** Self-serve developer-access opt-in (webhooks + API keys) is only open
+ * to paid tiers — free-tier users still need an admin grant. */
+export function canSelfServeDeveloperAccess(user: { tier: string }): boolean {
+  return user.tier !== "free";
+}