feat: add mind model with versioned personality, templates and self-model

Phase 2. Minds are rows with a slug, status (active/disabled/archived),
cognitive configuration and a pointer to the current personality version.
Personalities are structured (identity, values, traits, communication,
behaviour, free text) with a deterministic Brief() used by prompts and the
editor preview. Every change appends a personality_versions row protected
by the append-only trigger; restore copies an old version forward.
Templates carry reusable personalities; minds record their overrides so a
template can be re-applied without losing mind-specific edits. The
self-model starts with structural limitations the mind cannot drop
(no policy changes, no influence over shutdown, no cross-mind access).

API, UI (list, overview, editor with sliders/diff/history/import/export,
template editor) and noemactl mind/template commands. All mutations are
audited with field-level diffs.

CHANGELOG.md

@@ -5,5 +5,6 @@ All notable changes to Noema are recorded here. Format follows Keep a Changelog;
 ## [Unreleased]
 
 ### Added
+- Phase 2 minds: structured personalities with append-only version history, diff, restore, templates with preserved overrides, self-model, mind lifecycle (create, clone, disable, archive), API, UI editor and CLI.
 - Phase 1 foundation: configuration, structured logging, metrics, migrations, local authentication (Argon2id, sessions, CSRF, lockout, roles, API tokens), audit log, JSON API skeleton, server-rendered admin UI with light/dark theme, `noemad` and `noemactl`.
 - Repository foundation: plan, architecture, security model, threat model, ADRs, Makefile, container files.