Add public AI prompt templates for websites.

Manage reusable templates in Super Admin, attach editable per-site prompts with Meshkee API public links that require no auth.

Co-authored-by: Cursor <cursoragent@cursor.com>

database/migrations/077_domain_ai_prompt_instances.sql

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+-- Per-website AI prompt instances (editable copies) with their own public links.
+
+CREATE TABLE IF NOT EXISTS domain_ai_prompts (
+  id                  BIGSERIAL PRIMARY KEY,
+  domain_id           BIGINT NOT NULL REFERENCES domains (id) ON DELETE CASCADE,
+  source_template_id  BIGINT REFERENCES ai_prompt_templates (id) ON DELETE SET NULL,
+  name                VARCHAR(255) NOT NULL,
+  body                TEXT NOT NULL,
+  public_id           VARCHAR(32) NOT NULL,
+  sort_order          INT NOT NULL DEFAULT 0,
+  created_at          TIMESTAMPTZ NOT NULL DEFAULT now(),
+  updated_at          TIMESTAMPTZ NOT NULL DEFAULT now(),
+  CONSTRAINT domain_ai_prompts_public_id_unique UNIQUE (public_id)
+);
+
+CREATE INDEX IF NOT EXISTS idx_domain_ai_prompts_domain_id
+  ON domain_ai_prompts (domain_id, sort_order, id);
+
+CREATE INDEX IF NOT EXISTS idx_domain_ai_prompts_source_template_id
+  ON domain_ai_prompts (source_template_id);
+
+CREATE OR REPLACE FUNCTION domain_ai_prompts_set_updated_at()
+RETURNS TRIGGER AS $$
+BEGIN
+  NEW.updated_at = now();
+  RETURN NEW;
+END;
+$$ LANGUAGE plpgsql;
+
+DROP TRIGGER IF EXISTS domain_ai_prompts_set_updated_at ON domain_ai_prompts;
+CREATE TRIGGER domain_ai_prompts_set_updated_at
+  BEFORE UPDATE ON domain_ai_prompts
+  FOR EACH ROW
+  EXECUTE FUNCTION domain_ai_prompts_set_updated_at();
+
+-- Copy existing assignments into editable instances (one public id each).
+DO $$
+DECLARE
+  r RECORD;
+  pid TEXT;
+BEGIN
+  IF EXISTS (
+    SELECT 1 FROM information_schema.tables
+    WHERE table_name = 'domain_ai_prompt_templates'
+  ) THEN
+    FOR r IN
+      SELECT
+        l.domain_id,
+        l.template_id,
+        l.sort_order,
+        t.name,
+        t.body
+      FROM domain_ai_prompt_templates l
+      JOIN ai_prompt_templates t ON t.id = l.template_id
+      ORDER BY l.domain_id, l.sort_order, l.template_id
+    LOOP
+      LOOP
+        pid := encode(gen_random_bytes(12), 'hex');
+        EXIT WHEN NOT EXISTS (
+          SELECT 1 FROM domain_ai_prompts WHERE public_id = pid
+        );
+      END LOOP;
+
+      INSERT INTO domain_ai_prompts (
+        domain_id, source_template_id, name, body, public_id, sort_order
+      ) VALUES (
+        r.domain_id, r.template_id, r.name, r.body, pid, r.sort_order
+      );
+    END LOOP;
+  END IF;
+END $$;
+
+DROP TABLE IF EXISTS domain_ai_prompt_templates;