docs: Phase 9 documentation roundup — close encryption-shaped doc gaps

Five documentation surfaces gained encryption awareness in this
sweep. Before this commit, the only place anyone could learn about
the at-rest encryption layer or the zero-knowledge opt-in was the
internal DATA_LAYER_AUDIT.md. New contributors and self-hosters
would never discover one of the most important features of the
product just by reading the standard onboarding docs.

apps/docs/src/content/docs/architecture/security.mdx (NEW)
----------------------------------------------------------
First-class user-facing security page in the Starlight site,
slotted into the Architecture sidebar between Authentication and
Backend.

Sections:
  - What's encrypted (overview table of 27 modules + the
    intentional plaintext carve-outs)
  - Standard mode flow with ASCII diagram
  - "What Mana CAN see" trust statements per mode
  - Zero-knowledge mode setup walkthrough (Steps component)
  - Unlock flow on a new device
  - Recovery code rotation
  - Deployment requirements (the loud MANA_AUTH_KEK warning)
  - Audit trail action vocabulary
  - Threat model summary table
  - Implementation file references with paths

services/mana-auth/CLAUDE.md
----------------------------
New "Encryption Vault" section under Key Endpoints, listing all 7
routes (status, init, key, rotate, recovery-wrap GET+DELETE,
zero-knowledge) with their HTTP method, path, error codes, and a
description. Mentions the three CHECK constraints + RLS + audit
table. Points readers at DATA_LAYER_AUDIT.md and the new
security.mdx for the deep dive.

Environment Variables block gains MANA_AUTH_KEK with a multi-line
comment explaining the openssl rand command + dev fallback warning.

apps/mana/CLAUDE.md
-------------------
Full rewrite. The existing file was from the Supabase era and
described things like @supabase/ssr, safeGetSession(), and a
five-table schema with users + organizations + teams that doesn't
exist any more. Replaced with the unified-app architecture:

  - Module system layout (collections.ts / queries.ts / stores/)
  - Mana Auth (Better Auth + EdDSA JWT) instead of Supabase
  - Local-first data layer with the full pipeline diagram
  - At-rest encryption section with the "when writing module code
    that touches sensitive fields" 4-step guide
  - Updated routing structure (no more separate /organizations,
    /teams routes)
  - Module store pattern code example
  - Reference document table at the bottom pointing at the audit,
    the new security.mdx, and the auth doc

Root CLAUDE.md
--------------
New "At-Rest Encryption (Phase 1–9)" subsection under the
Local-First Architecture section. Two-mode trust summary table,
production requirement for MANA_AUTH_KEK with the openssl command,
the "when writing module code" 4-step guide, and a reference
table. New contributors reading the root CLAUDE.md from top to
bottom now hit encryption naturally as part of the data layer
discussion.

.env.macmini.example
--------------------
MANA_AUTH_KEK was missing from the production env example
entirely — the macmini deployment would silently boot on the
32-zero-byte dev fallback if you copied this file. Added with a
multi-paragraph comment covering: how to generate, why it's
required, how to store securely (Docker secrets / KMS / Vault),
and the rotation caveat.

apps/docs/src/content/docs/deployment/self-hosting.mdx
------------------------------------------------------
Two changes:

  1. Added MANA_AUTH_KEK to the mana-auth service block in the
     Compose example with an inline comment pointing at the new
     section below.

  2. New "Encryption Vault Setup" H2 section with subsections:
     - Generating a KEK (with a fake example value labelled DO NOT
       USE — generate your own)
     - Securing the KEK (Docker secrets, KMS, systemd
       LoadCredential, anti-patterns)
     - "What if I lose the KEK?" — explains the data is
       unrecoverable by design and mitigation via zero-knowledge
       mode opt-in
     - KEK rotation — calls out the missing background re-wrap
       job as a known limitation

apps/docs/astro.config.mjs
--------------------------
Added "Security & Encryption" entry to the Architecture sidebar
between Authentication and Backend so the new page is reachable
from the docs nav.

Astro check: 0 errors, 0 warnings, 0 hints across 4 .astro files.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

.env.macmini.example

@@ -32,6 +32,22 @@ JWT_SECRET=your-jwt-secret-here
 JWT_PUBLIC_KEY=
 JWT_PRIVATE_KEY=
 
+# ============================================
+# Encryption Vault Key Encryption Key (KEK) — REQUIRED
+# ============================================
+# Wraps every user's master key in auth.encryption_vaults.
+# Generate with: openssl rand -base64 32
+#
+# Without a real value, mana-auth boots with a 32-zero-byte fallback
+# and prints a loud warning every startup. Production must set this.
+# Treat it like a database root password — store as a Docker secret,
+# KMS-injected env var, or Vault-served value.
+#
+# Rotation requires planned downtime today (no background re-wrap job
+# yet). The kek_id column on encryption_vaults is reserved for the
+# future migration path.
+MANA_AUTH_KEK=
+
 # ============================================
 # Supabase (optional, for legacy features)
 # ============================================