feat(frontend): provider OpenCode dynamique + saisie provider personnalisé (#92)

Le picker de provider OpenCode du first-run wizard consomme le
catalogue dynamique exposé par le backend et propose une option
« provider personnalisé » avec un formulaire de saisie libre
(id + clé API) quand le provider souhaité n'y figure pas.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/src/ports/index.ts

@@ -13,6 +13,7 @@ import type {
   AgentDrift,
   AgentProfile,
   AppExitWorkGuardState,
+  CustomProviderConfig,
   DomainEvent,
   EmbedderEngines,
   EmbedderProfile,
@@ -701,12 +702,18 @@ export interface CloneOpenCodeProfileFromSeedInput {
 export interface SaveOpenCodeProviderProfileInput {
   /** The profile to create or replace (by id). */
   profile: AgentProfile;
-  /** Provider id in the OpenCode registry (e.g. `"anthropic"`). */
+  /** Provider id — a catalogue entry, or a free-form id when {@link custom} is set. */
   providerId: string;
   /** Model name served by this provider. */
   model: string;
   /** Literal API key — sealed into the `SecretStore`, never persisted as-is. */
   apiKey: string;
+  /**
+   * Optional custom-provider configuration (ticket #92): an endpoint outside
+   * the OpenCode registry. Absent/`undefined` = known catalogue provider
+   * (unchanged behaviour).
+   */
+  custom?: CustomProviderConfig;
 }
 
 /**