feat(server): add authenticated remote access and desktop bootstrap

Adds cookie-based login with a bootstrap token flow for desktop apps, secures OpenCode instance traffic with per-instance Basic auth, and updates UI/plugin clients to use credentials.

packages/server/src/auth/session-manager.ts

@@ -0,0 +1,23 @@
+import crypto from "crypto"
+
+export interface SessionInfo {
+  id: string
+  createdAt: number
+  username: string
+}
+
+export class SessionManager {
+  private sessions = new Map<string, SessionInfo>()
+
+  createSession(username: string): SessionInfo {
+    const id = crypto.randomBytes(32).toString("base64url")
+    const info: SessionInfo = { id, createdAt: Date.now(), username }
+    this.sessions.set(id, info)
+    return info
+  }
+
+  getSession(id: string | undefined): SessionInfo | undefined {
+    if (!id) return undefined
+    return this.sessions.get(id)
+  }
+}