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.

public/logo.svg

@@ -0,0 +1,27 @@
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="60 -5 280 350" role="img" aria-label="hackerspace.sh logo">
+  <circle cx="200" cy="185" r="115" stroke="currentColor" fill="none" stroke-width="7" stroke-linecap="round" stroke-linejoin="round"/>
+  <ellipse cx="200" cy="185" rx="45" ry="115" stroke="currentColor" fill="none" stroke-width="4" stroke-linecap="round" stroke-linejoin="round"/>
+  <ellipse cx="200" cy="185" rx="85" ry="115" stroke="currentColor" fill="none" stroke-width="4" stroke-linecap="round" stroke-linejoin="round"/>
+  <line x1="85" y1="185" x2="315" y2="185" stroke="currentColor" fill="none" stroke-width="4" stroke-linecap="round" stroke-linejoin="round"/>
+  <ellipse cx="200" cy="133" rx="100" ry="28" stroke="currentColor" fill="none" stroke-width="4" stroke-linecap="round" stroke-linejoin="round"/>
+  <ellipse cx="200" cy="237" rx="100" ry="28" stroke="currentColor" fill="none" stroke-width="4" stroke-linecap="round" stroke-linejoin="round"/>
+  <g fill="currentColor" stroke="none">
+    <circle cx="85" cy="185" r="9"/><circle cx="85" cy="185" r="3.5" fill="#0c0c0c"/>
+    <circle cx="115" cy="185" r="7"/><circle cx="115" cy="185" r="2.5" fill="#0c0c0c"/>
+    <circle cx="155" cy="185" r="7"/><circle cx="155" cy="185" r="2.5" fill="#0c0c0c"/>
+    <circle cx="245" cy="185" r="7"/><circle cx="245" cy="185" r="2.5" fill="#0c0c0c"/>
+    <circle cx="285" cy="185" r="7"/><circle cx="285" cy="185" r="2.5" fill="#0c0c0c"/>
+    <circle cx="315" cy="185" r="9"/><circle cx="315" cy="185" r="3.5" fill="#0c0c0c"/>
+    <circle cx="200" cy="70" r="8"/><circle cx="200" cy="70" r="3" fill="#0c0c0c"/>
+    <circle cx="200" cy="300" r="8"/><circle cx="200" cy="300" r="3" fill="#0c0c0c"/>
+  </g>
+  <g>
+    <circle cx="145" cy="160" r="11" fill="#d4ff00"/>
+    <circle cx="145" cy="160" r="4.5" fill="#0c0c0c"/>
+    <circle cx="145" cy="160" r="16" stroke="#d4ff00" fill="none" stroke-width="2.5" stroke-linecap="round" stroke-linejoin="round"/>
+  </g>
+  <g>
+    <circle cx="260" cy="205" r="10" fill="#d4ff00"/>
+    <circle cx="260" cy="205" r="4" fill="#0c0c0c"/>
+  </g>
+</svg>