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.

components/safe-markdown.tsx

@@ -7,24 +7,21 @@ import rehypeSanitize, { defaultSchema } from 'rehype-sanitize'
 
 // Renders admin-authored markdown that MAY contain a constrained subset of raw
 // HTML. rehype-raw parses the HTML; rehype-sanitize then strips anything
-// dangerous (script, event handlers, javascript: URLs, etc). The author is a
-// space admin/board member, but a stored-XSS payload would still run in other
-// members' sessions within that tenant, so this is sanitized, not trusted.
+// dangerous. The author is a space admin/board member, but a stored-XSS or
+// UI-redress payload would still run in other members' sessions within that
+// tenant, so this is sanitized hard, not trusted:
+//   - no `iframe` (no unsandboxed third-party embeds / token theft frame)
+//   - no global `style` attribute (no full-viewport overlay redress)
+//   - links forced to safe protocols; rel/target locked down
 const schema = {
   ...defaultSchema,
   attributes: {
     ...defaultSchema.attributes,
-    '*': [...(defaultSchema.attributes?.['*'] ?? []), 'className', 'style'],
+    '*': [...(defaultSchema.attributes?.['*'] ?? []), 'className'],
     a: [...(defaultSchema.attributes?.a ?? []), 'target', 'rel'],
   },
-  tagNames: [
-    ...(defaultSchema.tagNames ?? []),
-    'iframe',
-  ],
-  // Allow only video embeds from well-known hosts; everything else dropped.
   protocols: {
     ...defaultSchema.protocols,
-    src: ['https'],
     href: ['https', 'http', 'mailto'],
   },
 }