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>

cli/package.json

@@ -19,6 +19,7 @@
     "@paperclip/db": "workspace:*",
     "@paperclip/server": "workspace:*",
     "@paperclip/shared": "workspace:*",
+    "drizzle-orm": "0.38.4",
     "dotenv": "^17.0.1",
     "commander": "^13.1.0",
     "picocolors": "^1.1.1"