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.

lib/auth-actions.ts

@@ -107,10 +107,38 @@ export async function joinSpace(formData: {
   // Use admin client for operations
   const admin = createAdminClient()
 
+  const code = formData.inviteCode.trim().toUpperCase()
+
+  // Try the new multi-code invites table first. Falls back to the legacy
+  // spaces.invite_code (a permanent default) if the code isn't found there.
+  let invite: { id: string; space_id: string; max_uses: number | null; uses_count: number; expires_at: string | null; is_enabled: boolean } | null = null
+  const { data: inviteRow } = await admin
+    .from('space_invites')
+    .select('id, space_id, max_uses, uses_count, expires_at, is_enabled')
+    .eq('code', code)
+    .maybeSingle()
+  if (inviteRow) invite = inviteRow as typeof invite
+
+  let spaceId: string | null = null
+  if (invite) {
+    if (!invite.is_enabled) return { error: 'This invite is disabled.' }
+    if (invite.expires_at && new Date(invite.expires_at) < new Date()) return { error: 'This invite has expired.' }
+    if (invite.max_uses !== null && invite.uses_count >= invite.max_uses) return { error: 'This invite has reached its use cap.' }
+    spaceId = invite.space_id
+  } else {
+    const { data: legacy } = await admin
+      .from('spaces')
+      .select('id')
+      .eq('invite_code', code)
+      .maybeSingle()
+    if (!legacy) return { error: 'Invalid invite code' }
+    spaceId = legacy.id
+  }
+
   const { data: space, error: lookupErr } = await admin
     .from('spaces')
     .select('id, require_approval')
-    .eq('invite_code', formData.inviteCode.trim().toUpperCase())
+    .eq('id', spaceId)
     .single()
 
   if (lookupErr || !space) return { error: 'Invalid invite code' }
@@ -130,6 +158,14 @@ export async function joinSpace(formData: {
 
   if (memberErr) return { error: memberErr.message }
 
+  // Increment invite usage counter for the multi-code path.
+  if (invite) {
+    await admin
+      .from('space_invites')
+      .update({ uses_count: invite.uses_count + 1 })
+      .eq('id', invite.id)
+  }
+
   return { success: true }
 }