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.

migrations/0002_minds.down.sql

@@ -0,0 +1,4 @@
+DROP TABLE IF EXISTS self_models;
+DROP TABLE IF EXISTS personality_versions;
+DROP TABLE IF EXISTS personality_templates;
+DROP TABLE IF EXISTS minds;

migrations/0002_minds.up.sql

@@ -0,0 +1,50 @@
+-- Minds, personality versions (append-only), templates, self-models.
+
+CREATE TABLE minds (
+  id                   uuid PRIMARY KEY,
+  slug                 text NOT NULL,
+  display_name         text NOT NULL,
+  status               text NOT NULL DEFAULT 'active' CHECK (status IN ('active','disabled','archived')),
+  config               jsonb NOT NULL DEFAULT '{}'::jsonb,
+  notes                text NOT NULL DEFAULT '',
+  personality_version  integer NOT NULL DEFAULT 0,
+  forked_from_mind     uuid REFERENCES minds(id),
+  forked_from_snapshot uuid,
+  cloned_from_mind     uuid REFERENCES minds(id),
+  created_at           timestamptz NOT NULL DEFAULT now(),
+  updated_at           timestamptz NOT NULL DEFAULT now()
+);
+CREATE UNIQUE INDEX minds_slug_idx ON minds (lower(slug));
+
+CREATE TABLE personality_templates (
+  id          uuid PRIMARY KEY,
+  name        text NOT NULL,
+  description text NOT NULL DEFAULT '',
+  personality jsonb NOT NULL,
+  created_at  timestamptz NOT NULL DEFAULT now(),
+  updated_at  timestamptz NOT NULL DEFAULT now()
+);
+CREATE UNIQUE INDEX personality_templates_name_idx ON personality_templates (lower(name));
+
+-- Every personality change is a new row; minds.personality_version points at
+-- the current one. Rollback writes a new version copying an older one.
+CREATE TABLE personality_versions (
+  id          uuid PRIMARY KEY,
+  mind_id     uuid NOT NULL REFERENCES minds(id),
+  version     integer NOT NULL,
+  personality jsonb NOT NULL,        -- effective personality
+  template_id uuid REFERENCES personality_templates(id),
+  overrides   jsonb NOT NULL DEFAULT '{}'::jsonb, -- mind-specific deviations from the template
+  change_note text NOT NULL DEFAULT '',
+  created_by  text NOT NULL DEFAULT '',
+  created_at  timestamptz NOT NULL DEFAULT now(),
+  UNIQUE (mind_id, version)
+);
+CREATE TRIGGER personality_versions_append_only BEFORE UPDATE OR DELETE ON personality_versions
+  FOR EACH ROW EXECUTE FUNCTION noema_forbid_change();
+
+CREATE TABLE self_models (
+  mind_id    uuid PRIMARY KEY REFERENCES minds(id),
+  model      jsonb NOT NULL,
+  updated_at timestamptz NOT NULL DEFAULT now()
+);