Add Phase 6: multi-server admin panel (server registry + settings)

Gate a new /api/admin/* route set (register/list/update/delete servers)
behind a single shared MCMAPPER_ADMIN_TOKEN header, and add a /admin
frontend page (Alpine) to unlock, register new servers, and edit
authMode/anonymousChatAllowed/waypointFormat per server — these columns
already existed but were only editable via direct DB edit until now.

Written test-first per the project's TDD workflow: admin.ts's domain
logic, the index.ts route wiring, and a new e2e/tests/admin.spec.ts
covering the token gate and register/edit/delete round trip through the
real browser UI.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_015tKdPZt78zbPUZMXWzKEKt

e2e/config.ts

@@ -31,6 +31,10 @@ export const MINIO_SECRET_KEY = "mcmapper-e2e-only";
 
 export const PROXY_ORIGIN = `http://localhost:${PROXY_PORT}`;
 
+// Fixed, not random: admin.spec.ts needs to know it up front, and this only ever gates the
+// throwaway e2e api instance.
+export const ADMIN_TOKEN = "e2e-admin-token";
+
 export const STATE_FILE = join(import.meta.dirname, ".e2e-state.json");
 
 export type E2eState = {
@@ -41,6 +45,7 @@ export type E2eState = {
   serverToken: string;
   sessionToken: string;
   accountId: string;
+  adminToken: string;
 };
 
 // Read by spec files — by the time tests run, global-setup.ts has already written this.