feat: selectable pairing-notify provider (discord optional, add fabric)

Pairing-code delivery was hardwired to Discord DM (notifyBotToken +
adminUserId required). Make the provider config-selectable.

- core/config.ts: add notifyProvider ("discord"|"fabric", default
  "discord" for back-compat); discord fields required only for discord;
  add fabric block (centerApiBase/apiKey/guildNodeId/channelId) required
  only for fabric
- notifications/types.ts: neutral PairingNotificationService interface
  (DiscordNotificationService kept as back-compat alias)
- notifications/fabric.ts: post the pairing message to a Fabric channel
  (agent/login -> guild token -> POST messages); self-contained, no
  Fabric plugin dependency
- notifications/factory.ts: select provider from config
- core/runtime.ts: wire via factory
- openclaw.plugin.json: notifyProvider enum + fabric object; drop
  notifyBotToken/adminUserId from required (conditional in code)
- tests: fabric notifier + provider-selection config (80 passing)

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

plugin/core/config.ts

@@ -1,7 +1,22 @@
+export type NotifyProvider = "discord" | "fabric";
+
+export interface FabricNotifyConfig {
+  centerApiBase: string;
+  apiKey: string;
+  guildNodeId: string;
+  channelId: string;
+}
+
 export interface YonexusServerConfig {
   followerIdentifiers: string[];
-  notifyBotToken: string;
-  adminUserId: string;
+  /** Pairing-code delivery provider. Default: "discord" (back-compat). */
+  notifyProvider: NotifyProvider;
+  /** Required only when notifyProvider === "discord". */
+  notifyBotToken?: string;
+  /** Required only when notifyProvider === "discord". */
+  adminUserId?: string;
+  /** Required only when notifyProvider === "fabric". */
+  fabric?: FabricNotifyConfig;
   listenHost?: string;
   listenPort: number;
   publicWsUrl?: string;
@@ -67,14 +82,45 @@ export function validateYonexusServerConfig(raw: unknown): YonexusServerConfig {
     issues.push("followerIdentifiers must not contain duplicates");
   }
 
-  const rawNotifyBotToken = source.notifyBotToken;
-  if (!isNonEmptyString(rawNotifyBotToken)) {
-    issues.push("notifyBotToken is required");
+  const rawNotifyProvider = source.notifyProvider;
+  let notifyProvider: NotifyProvider = "discord";
+  if (rawNotifyProvider === undefined || rawNotifyProvider === null) {
+    notifyProvider = "discord";
+  } else if (rawNotifyProvider === "discord" || rawNotifyProvider === "fabric") {
+    notifyProvider = rawNotifyProvider;
+  } else {
+    issues.push('notifyProvider must be "discord" or "fabric"');
   }
 
+  // Discord fields — required only for the discord provider.
+  const rawNotifyBotToken = source.notifyBotToken;
   const rawAdminUserId = source.adminUserId;
-  if (!isNonEmptyString(rawAdminUserId)) {
-    issues.push("adminUserId is required");
+  if (notifyProvider === "discord") {
+    if (!isNonEmptyString(rawNotifyBotToken)) {
+      issues.push('notifyBotToken is required when notifyProvider is "discord"');
+    }
+    if (!isNonEmptyString(rawAdminUserId)) {
+      issues.push('adminUserId is required when notifyProvider is "discord"');
+    }
+  }
+
+  // Fabric fields — required only for the fabric provider.
+  let fabric: FabricNotifyConfig | undefined;
+  if (notifyProvider === "fabric") {
+    const f = (source.fabric && typeof source.fabric === "object"
+      ? source.fabric
+      : {}) as Record<string, unknown>;
+    const centerApiBase = normalizeOptionalString(f.centerApiBase);
+    const apiKey = normalizeOptionalString(f.apiKey);
+    const guildNodeId = normalizeOptionalString(f.guildNodeId);
+    const channelId = normalizeOptionalString(f.channelId);
+    if (!centerApiBase) issues.push("fabric.centerApiBase is required when notifyProvider is \"fabric\"");
+    if (!apiKey) issues.push("fabric.apiKey is required when notifyProvider is \"fabric\"");
+    if (!guildNodeId) issues.push("fabric.guildNodeId is required when notifyProvider is \"fabric\"");
+    if (!channelId) issues.push("fabric.channelId is required when notifyProvider is \"fabric\"");
+    if (centerApiBase && apiKey && guildNodeId && channelId) {
+      fabric = { centerApiBase, apiKey, guildNodeId, channelId };
+    }
   }
 
   const rawListenPort = source.listenPort;
@@ -93,14 +139,18 @@ export function validateYonexusServerConfig(raw: unknown): YonexusServerConfig {
     throw new YonexusServerConfigError(issues);
   }
 
-  const notifyBotToken = rawNotifyBotToken as string;
-  const adminUserId = rawAdminUserId as string;
   const listenPort = rawListenPort as number;
 
   return {
     followerIdentifiers,
-    notifyBotToken: notifyBotToken.trim(),
-    adminUserId: adminUserId.trim(),
+    notifyProvider,
+    notifyBotToken: isNonEmptyString(rawNotifyBotToken)
+      ? rawNotifyBotToken.trim()
+      : undefined,
+    adminUserId: isNonEmptyString(rawAdminUserId)
+      ? rawAdminUserId.trim()
+      : undefined,
+    fabric,
     listenHost,
     listenPort,
     publicWsUrl