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/changelog.ts

@@ -1,5 +1,5 @@
 // Mirrors CHANGELOG.md at the repo root — update both together.
-export const APP_VERSION = "0.71.0";
+export const APP_VERSION = "0.72.0";
 
 export type ChangelogEntry = {
   version: string;
@@ -11,6 +11,13 @@ export type ChangelogEntry = {
 };
 
 export const CHANGELOG: ChangelogEntry[] = [
+  {
+    version: "0.72.0",
+    date: "2026-07-23 09:30",
+    added: [
+      "Developer access (webhooks + API keys) is now self-serve for any paid-tier user, free of charge — enable it yourself in Settings instead of waiting on an admin. Free tier still needs an admin grant. BYOK is now a fully separate permission, admin-only, unaffected by the self-serve change.",
+    ],
+  },
   {
     version: "0.71.0",
     date: "2026-07-22 10:00",