refactor: dead-code cleanup + drop the lib/types shim (slice 9)

- Delete orphaned components (theme-provider, task-claim-button), the unused
  roleDisplayName helper, the fully-dead cleanupRateLimits, the 6 never-imported
  validation schemas (signIn/signUp/createSpace/joinSpace — a replaced auth flow;
  proposalStatuses; updateAreaLeadRoleSchema).
- Migrate all @/lib/types importers to the canonical @/types/domain and delete
  the compatibility shim.

tsc 0, 635 tests green, lint clean.

Co-Authored-By: Claude Opus 4.8 (1M context) <[email protected]>

app/(app)/policies/[slug]/page.tsx

@@ -1,7 +1,7 @@
 import Link from 'next/link'
 import { redirect, notFound } from 'next/navigation'
 import { createClient } from '@/lib/supabase/server'
-import type { Policy } from '@/lib/types'
+import type { Policy } from '@/types/domain'
 import { PolicyActions } from './policy-actions'
 import { MarkdownBody } from '@/components/markdown'
 import { CommentThread } from '@/components/comments/comment-thread'

app/(app)/policies/[slug]/policy-actions.tsx

@@ -4,7 +4,7 @@ import { useState, useTransition } from 'react'
 import { useRouter } from 'next/navigation'
 import { supersedePolicy, updatePolicyStatus } from '@/lib/actions'
 import { policyStatuses } from '@/lib/validations'
-import type { Policy } from '@/lib/types'
+import type { Policy } from '@/types/domain'
 
 export function PolicyActions({ policy }: { policy: Policy }) {
   const router = useRouter()

app/(app)/policies/page.tsx

@@ -1,7 +1,7 @@
 import Link from 'next/link'
 import { redirect } from 'next/navigation'
 import { createClient } from '@/lib/supabase/server'
-import type { Policy, PolicyStatus } from '@/lib/types'
+import type { Policy, PolicyStatus } from '@/types/domain'
 import { PageTitle } from '@/components/ui/page-title'
 
 export const dynamic = 'force-dynamic'