feat: forum, polymorphic comments, custom tiers, multi-invite, secrets encryption

Big feature batch driven by the super-audit findings and the user's
follow-up requests.

Schema migration 021 (folded into schema.sql Section 13):
- forum_threads + polymorphic comments table keyed on (entity_type,
  entity_id). Entity types: forum_thread, proposal, incident, policy.
  Trigger maintains forum_threads.comment_count and last_comment_at.
- space_tiers per-space with monthly_price_cents, billing_cadence,
  is_system, sort_order. Trigger seeds plus/basic/associate on every
  space INSERT and backfills existing spaces. space_members.tier_id FK
  added and backfilled from the legacy enum value.
- space_role_labels (rename/recolor built-in roles per space).
  space_custom_roles + space_member_custom_roles for non-privileged
  extra labels. RLS gates by admin/board.
- space_invites: multi-code invites with expires_at, max_uses,
  uses_count, is_enabled. Legacy spaces.invite_code backfilled as a
  permanent enabled invite.
- secrets.encrypted_value bytea + encryption_version. Secrets RLS
  tightened. New comms_channels INSERT policy: any member can create;
  default channels are protected from deletion.
- knowledge_base.render_markdown boolean (default true).

Secrets encryption-at-rest:
- AES-256-GCM in lib/secrets/crypto.ts. Master key from
  SECRETS_ENCRYPTION_KEY env (64 hex chars).
- New revealSecret(id) server action: only path to plaintext, writes
  secret.revealed to activity_log.
- /ops/page.tsx no longer selects value or encrypted_value on the list
  endpoint - the original screenshot bug where ciphertext was already
  in the page bundle before "Reveal" is fixed.

UI:
- /forum index, /forum/new, /forum/[id]. Pin/lock/delete actions for
  admin/board.
- CommentThread component embedded on /proposals/[id], /incidents/[id],
  /policies/[slug]. Markdown rendering via react-markdown + remark-gfm.
- /comms sidebar: inline "+ New channel" form.
- /ops KB: row click opens markdown-rendering viewer modal.
- /settings: new Tiers tab and Invites tab. Inline price edit and
  archive/delete on tiers; copy/enable/disable/delete on invites.
- AtlasLogo replaces the terminal icon on the landing nav and footer.
  public/logo.svg wired as the favicon in app/layout.tsx metadata.
- Sidebar has a Forum nav link.

Server actions added:
- lib/actions/forum.ts, comms.ts, tiers.ts, roles.ts, invites.ts.
- lib/actions/secrets.ts rewritten with updateSecret + revealSecret.

Auth flow:
- joinSpace honors codes from space_invites first (enabled, expiry,
  use cap), falls back to legacy spaces.invite_code, increments
  uses_count on success.

Env:
- SECRETS_ENCRYPTION_KEY documented in .env.example and set on the
  Droplet's /opt/hackerspace-ops/.env.production.

README: live site link added (https://hackerspace.sh).

266/266 unit tests pass. Production build clean. Migration 021 will be
applied on the next deploy via /opt/hackerspace-ops/deploy.sh's
idempotent migration runner.

app/(landing)/page.tsx

@@ -2,6 +2,7 @@
 
 import { useState, useEffect } from 'react'
 import Link from 'next/link'
+import { AtlasLogo } from '@/components/resources/atlas-logo'
 
 // Icons
 function IcoUsers({ className }: { className?: string }) {
@@ -318,7 +319,7 @@ export default function LandingPage() {
       <nav className="border-b border-border bg-sidebar">
         <div className="max-w-6xl mx-auto px-4 md:px-6 py-3 flex items-center justify-between gap-4">
           <div className="flex items-center gap-2 min-w-0">
-            <IcoTerminal className="w-5 h-5 text-primary shrink-0" />
+            <AtlasLogo className="w-6 h-6 text-primary shrink-0" />
             <span className="font-mono text-sm font-bold text-white truncate">hackerspace.sh</span>
           </div>
           <div className="flex items-center gap-2 shrink-0">
@@ -515,7 +516,7 @@ export default function LandingPage() {
         <div className="max-w-6xl mx-auto px-4 md:px-6 py-8">
           <div className="flex flex-col md:flex-row items-start md:items-center justify-between gap-4">
             <div className="flex items-center gap-2">
-              <IcoTerminal className="w-4 h-4 text-primary" />
+              <AtlasLogo className="w-5 h-5 text-primary" />
               <span className="font-mono text-xs text-sidebar-foreground">hackerspace.sh</span>
             </div>
             <div className="flex items-center gap-4">