docs: add entity ID preservation and anti-enumeration patterns

[moltboie]

Add two patterns to DEVELOPMENT.md extracted from recent merged PRs:

Entity ID Preservation During Sync

From PR #134 — when cloning entities for sync, capture original references before mutation to avoid lookup failures with new UUIDs.

Authentication: Anti-Enumeration

From PR #136 — generic error messages and constant-time dummy bcrypt comparison to prevent username enumeration and timing attacks.

E2E Testing

Documentation-only change. Verified markdown renders correctly.

[moltboie]

Self-Review

Discussion thread status:

• No prior thread.

Checked:

• Logic — Documents two patterns: (1) Entity ID preservation during sync — capture original IDs before cloning; (2) Anti-enumeration via constant-time bcrypt dummy compare and generic error messages.
• Types — Docs only.
• Quality — Good examples with explicit bad/good contrast. References specific PRs (#134, #136) for traceability.
• Maintainability — Self-contained patterns. Clear enough to follow without looking up the referenced PRs.
• Security — Anti-enumeration section is particularly valuable: generic error messages + dummy bcrypt compare is the correct defense against user enumeration via timing.
• Tests — N/A.
• Blockers — None.

Issues found:

• None.

Confidence: High