feat(ai): add the storage for an OpenAI-compatible gateway provider

Three dedicated User columns — base URL, optional bearer, model — for a
provider whose endpoint the user chooses. They are separate from the
OpenAI columns on purpose: the OpenAI arm pins api.openai.com, so it must
share no column with a user-supplied host, and a gateway must never
receive the key issued for OpenAI.

The bearer joins the encrypted-column registry and the rotation script;
the three columns join the account-wipe reset set.

prisma/migrations/0280_openai_compatible_provider/migration.sql

@@ -0,0 +1,17 @@
+-- The OpenAI-compatible gateway provider (#470): a user-configured endpoint
+-- that speaks `/v1/chat/completions` — LiteLLM, OpenRouter, vLLM, or anything
+-- else on that wire — with its own base URL, its own optional bearer, and its
+-- own model.
+--
+-- Three dedicated columns instead of reusing `ai_base_url` / the OpenAI key.
+-- The OpenAI arm pins `api.openai.com` on purpose, so it must have no column
+-- in common with a provider whose host the user chooses; and the gateway must
+-- never receive the key the user issued for OpenAI. Separating the storage
+-- makes both properties structural rather than a comment someone can delete.
+--
+-- All three are nullable and additive: an install that never configures the
+-- provider carries three NULLs and resolves exactly as before.
+
+ALTER TABLE "users" ADD COLUMN "ai_compat_base_url" TEXT;
+ALTER TABLE "users" ADD COLUMN "ai_compat_key_encrypted" TEXT;
+ALTER TABLE "users" ADD COLUMN "ai_compat_model" TEXT;

prisma/schema.prisma

@@ -311,6 +311,18 @@ model User {
   // before storage.
   aiOpenaiKeyEncrypted     String?              @map("ai_openai_key_encrypted")
 
+  // v1.33.1 (#470) — the OpenAI-compatible gateway provider (LiteLLM,
+  // OpenRouter, vLLM, any endpoint speaking `/v1/chat/completions`).
+  // Three DEDICATED columns rather than a reuse of `aiBaseUrl` /
+  // `aiOpenaiKeyEncrypted`: the OpenAI arm pins `api.openai.com` and must
+  // never be able to read a user-supplied host, and the gateway credential
+  // must never be the OpenAI key. Separate columns make that structural
+  // instead of a comment. The base URL passes the same SSRF floor as the
+  // Local provider (`isPublicUrl` unless the operator allowlisted the host).
+  aiCompatBaseUrl          String?              @map("ai_compat_base_url")
+  aiCompatKeyEncrypted     String?              @map("ai_compat_key_encrypted")
+  aiCompatModel            String?              @map("ai_compat_model")
+
   // v1.4.16 phase B5b — ordered fallback chain for multi-provider AI
   // redundancy. Each entry is `{ providerType, priority, enabled }`,
   // sorted by ascending priority at runtime. Credentials live in the