docs: decide multi-person ZK sharing ADR; reconcile jwt/encryption docs

Rewrite the encryption/persona/JWT docs to match the implemented code and
record the multi-person sharing design.

- multi-person-sharing.md (NEW): ADR for per-profile DEK + X25519 envelope
  sharing. All five original open questions resolved 2026-07-18. Covers
  divorced-parents, pets, graduation, and elderly-parent care; adds an
  admin permission tier for owner-incapacity. Decided, not yet implemented.
  (#3)
- encryption.md: full rewrite to the implemented wrapped-DEK / Web Crypto
  model; the old version described ZK encryption as 'planned'. (#4)
- jwt-authentication-decision.md: rewritten to match implementation
  (PBKDF2 not bcrypt, no Redis, token_version revocation, real Claims).
  Original aspirational content preserved in a History section. (#4)
- PERSONA_AND_FAMILY_MANAGEMENT.md: 'Current reality' section added, old
  'Implementation Status' marked superseded, encryption section corrected. (#4)
- ENCRYPTION_UPDATE_SUMMARY.md: archived (changelog for a rewrite that
  itself went stale). (#4)
- ADR README index updated for the new + reconciled entries.

docs/product/ENCRYPTION_UPDATE_SUMMARY.md

@@ -1,105 +0,0 @@
-# Encryption.md Update Summary
-
-**Date**: 2026-03-09  
-**File**: docs/product/encryption.md  
-**Update**: Added Rust implementation examples and current status
-
----
-
-## Changes Made
-
-### 1. Added Implementation Status Section 🆕
-- Currently implemented features marked with ✅
-- Planned features marked with 📋
-- Clear distinction between design and implementation
-
-### 2. Added Rust Implementation Examples 🆕
-**Current Security Features**:
-- JWT Authentication Service (actual code from `backend/src/auth/mod.rs`)
-- Password Hashing with PBKDF2 (100,000 iterations)
-- Rate Limiting Middleware (tower-governor)
-- Account Lockout Service (exponential backoff)
-- Security Audit Logger (MongoDB logging)
-
-**Proposed Encryption Features**:
-- Encryption Service design (AES-256-GCM)
-- Encrypted Health Data Model
-- Deterministic Encryption for searchable fields
-- Key Management Strategy
-- Shareable Links implementation
-
-### 3. Updated Code Examples
-- Replaced JavaScript/Node.js examples with Rust
-- Used actual implementation from Normogen codebase
-- Added real-world examples from existing code
-- Maintained theoretical examples for planned features
-
-### 4. Added Comparison Table
-- Current Implementation vs Proposed
-- Implementation status for all features
-- Priority and complexity ratings
-
-### 5. Updated Dependencies
-- Listed currently used crates (jsonwebtoken, pbkdf2, etc.)
-- Proposed additions for encryption features
-
----
-
-## File Statistics
-
-### Before
-- Size: 32KB
-- Lines: 1,248
-- Language: JavaScript/Node.js examples
-- Focus: Theoretical design
-
-### After
-- Size: 28KB (slightly smaller)
-- Lines: ~1,100
-- Language: Rust examples (matching backend)
-- Focus: Current implementation + future design
-
----
-
-## Key Improvements
-
-1. **Accurate**: Reflects actual implementation status
-2. **Rust-focused**: Matches backend technology
-3. **Practical**: Real code from codebase, not just theory
-4. **Clear**: Distinguishes between implemented and planned
-5. **Comprehensive**: Covers current security + future encryption
-
----
-
-## Implementation Coverage
-
-### Currently Implemented ✅
-- JWT authentication (15min access, 30day refresh)
-- PBKDF2 password hashing (100K iterations)
-- Rate limiting (15 req/s, burst 30)
-- Account lockout (5 attempts, exponential backoff)
-- Security audit logging
-- Session management
-
-### Planned for Future 📋
-- End-to-end encryption
-- Client-side encryption
-- Zero-knowledge encryption
-- Shareable links with embedded passwords
-- Key rotation
-
----
-
-## Next Steps
-
-1. ✅ Document current security implementation
-2. ✅ Add Rust code examples
-3. 📋 Implement zero-knowledge encryption (Phase 3+)
-4. 📋 Add client-side encryption
-5. 📋 Implement shareable links
-
----
-
-**Update Complete**: 2026-03-09  
-**Status**: Documentation now matches actual implementation  
-**Quality**: Improved accuracy and relevance