feat: add auth/access foundation - deps, DB schema, shared types, and config

Add Better Auth, drizzle-orm, @dnd-kit, and remark-gfm dependencies.
Introduce DB schema for auth tables (user, session, account, verification),
company memberships, instance user roles, permission grants, invites, and
join requests. Add assigneeUserId to issues. Extend shared config schema
with deployment mode/exposure/auth settings, add access types and validators,
and wire up new API path constants.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

packages/shared/src/validators/access.ts

@@ -0,0 +1,49 @@
+import { z } from "zod";
+import {
+  INVITE_JOIN_TYPES,
+  JOIN_REQUEST_STATUSES,
+  JOIN_REQUEST_TYPES,
+  PERMISSION_KEYS,
+} from "../constants.js";
+
+export const createCompanyInviteSchema = z.object({
+  allowedJoinTypes: z.enum(INVITE_JOIN_TYPES).default("both"),
+  expiresInHours: z.number().int().min(1).max(24 * 30).optional().default(72),
+  defaultsPayload: z.record(z.string(), z.unknown()).optional().nullable(),
+});
+
+export type CreateCompanyInvite = z.infer<typeof createCompanyInviteSchema>;
+
+export const acceptInviteSchema = z.object({
+  requestType: z.enum(JOIN_REQUEST_TYPES),
+  agentName: z.string().min(1).max(120).optional(),
+  adapterType: z.string().min(1).max(120).optional(),
+  capabilities: z.string().max(4000).optional().nullable(),
+  agentDefaultsPayload: z.record(z.string(), z.unknown()).optional().nullable(),
+});
+
+export type AcceptInvite = z.infer<typeof acceptInviteSchema>;
+
+export const listJoinRequestsQuerySchema = z.object({
+  status: z.enum(JOIN_REQUEST_STATUSES).optional(),
+  requestType: z.enum(JOIN_REQUEST_TYPES).optional(),
+});
+
+export type ListJoinRequestsQuery = z.infer<typeof listJoinRequestsQuerySchema>;
+
+export const updateMemberPermissionsSchema = z.object({
+  grants: z.array(
+    z.object({
+      permissionKey: z.enum(PERMISSION_KEYS),
+      scope: z.record(z.string(), z.unknown()).optional().nullable(),
+    }),
+  ),
+});
+
+export type UpdateMemberPermissions = z.infer<typeof updateMemberPermissionsSchema>;
+
+export const updateUserCompanyAccessSchema = z.object({
+  companyIds: z.array(z.string().uuid()).default([]),
+});
+
+export type UpdateUserCompanyAccess = z.infer<typeof updateUserCompanyAccessSchema>;