fix(security): close member self-escalation + harden after full audit

Full-application audit (5 parallel read-only audits). Two agent
"blockers" were false alarms and verified as already-correct. Real
findings fixed:

- Self-escalation (BLOCKER): migration 024 + schema.sql section 16
  extend prevent_member_self_role_change to also block a
  non-privileged member changing their own tier_id (self tier
  upgrade) and onboarding_completed_at (skipping required
  code-of-conduct via a raw PostgREST call). finishOnboarding and
  skipOnboarding now set onboarding_completed_at through the service
  client AFTER their server-side required-steps check, so the
  legitimate path is unaffected.
- Cross-tenant write scoping: added .eq('space_id', member.space_id)
  to updateForumThread, deleteForumThread, editComment, deleteComment,
  deleteChannel, renameChannel (RLS-only -> defence-in-depth).
- generateInviteCode: crypto.getRandomValues, widened to 8 chars
  (was Math.random, ~21 bits, enumerable under the join rate limit).
- SafeMarkdown: dropped iframe and the global style attribute
  (no unsandboxed embeds / UI-redress); markdown + safe HTML stay.
- /settings: server-side admin redirect before fetching space and
  integration config (was client-hidden only).
- app/(app)/layout.tsx: export const dynamic = 'force-dynamic'.
- Bounded queries: loadComments .limit(500), tasks .limit(2000).

Backlog from the audit is tracked in HANDOFF (import Zod schemas,
types/database.ts + docs regen, email lowercasing, unauthorized-
handling consistency, KB-modal ACL hookup).

271/271 tests pass. Build clean. Migrations 023 + 024 idempotent,
apply via deploy.sh on next deploy.

lib/actions/comms.ts

@@ -55,12 +55,14 @@ export async function deleteChannel(channelId: string) {
   const supabase = await createClient()
   const auth = await requireMember(supabase)
   if (!auth.ok) return { error: auth.error }
+  const { member } = auth
 
   // Default channels are protected at the RLS layer too.
   const { error, count } = await supabase
     .from('comms_channels')
     .delete({ count: 'exact' })
     .eq('id', v.data)
+    .eq('space_id', member.space_id)
 
   if (error) return { error: error.message }
   if (count === 0) return { error: 'Cannot delete this channel' }
@@ -77,11 +79,13 @@ export async function renameChannel(channelId: string, name: string, description
   const supabase = await createClient()
   const auth = await requireMember(supabase)
   if (!auth.ok) return { error: auth.error }
+  const { member } = auth
 
   const { error } = await supabase
     .from('comms_channels')
     .update({ name: v.data.name, description: v.data.description ?? null })
     .eq('id', idCheck.data)
+    .eq('space_id', member.space_id)
 
   if (error) return { error: error.message }
   revalidatePath('/comms')