feat(analytics): add product catalog data foundation

Add the per-account product reference list (product_catalog_entries) that the
LLM conversation classifier will use to tag conversations with the exact
product/group from the catalog (group > subgroup > product + display name +
aliases) instead of free-form product guessing, keeping tags consistent for
reporting.

- product_catalog_entries: unique (account_id, group_name, product_name);
  accounts store imports from CSV/XLSX/copy-paste (admin-only per-account).
- ProductCatalogEntry: belongs_to :account, presence + scoped uniqueness,
  aliases getter, tag_hierarchy returning [group, subgroup?, product].

Approved by independent five-key pre-commit review deleg_c431a86d
(passed=true, blocking arrays empty).

app/models/product_catalog_entry.rb

@@ -0,0 +1,37 @@
+# == Schema Information
+#
+# Table name: product_catalog_entries
+#
+#  id             :bigint           not null, primary key
+#  account_id     :bigint           not null
+#  group_name     :string           not null
+#  subgroup_name  :string
+#  product_name   :string           not null
+#  display_name   :string
+#  aliases        :jsonb            default([]), not null
+#  created_at     :datetime         not null
+#  updated_at     :datetime         not null
+#
+class ProductCatalogEntry < ApplicationRecord
+  belongs_to :account
+
+  validates :account_id, presence: true
+  validates :group_name, presence: true
+  validates :product_name, presence: true
+  validates :product_name, uniqueness: { scope: %i[account_id group_name] }
+
+  # JSONB aliases always an Array; never leak nil.
+  def aliases
+    self[:aliases] || []
+  end
+
+  # Return the full tag to write onto a conversation for a matched product.
+  # Nested group > subgroup > product are emitted so LLM falling back to a
+  # coarser level can still produce a consistent hierarchy.
+  def tag_hierarchy
+    parts = [group_name]
+    parts << subgroup_name if subgroup_name.present?
+    parts << product_name
+    parts
+  end
+end

db/migrate/20260819000002_create_product_catalog_entries.rb

@@ -0,0 +1,18 @@
+class CreateProductCatalogEntries < ActiveRecord::Migration[7.1]
+  def change
+    create_table :product_catalog_entries do |t|
+      t.bigint :account_id, null: false
+      t.string :group_name, null: false      # top-level: กลุ่มสินค้าใหญ่
+      t.string :subgroup_name                # กลุ่มสินค้าย่อย (optional)
+      t.string :product_name, null: false    # ตัวสินค้า
+      t.string :display_name                 # ชื่อสินค้าที่แสดง (optional, for matching)
+      t.jsonb :aliases, default: [], null: false  # alternate spellings/synonyms for fuzzy LLM matching
+      t.timestamps
+    end
+
+    add_index :product_catalog_entries, [:account_id, :group_name, :product_name], unique: true,
+              name: 'index_pce_on_account_group_product'
+    add_index :product_catalog_entries, :account_id
+    add_index :product_catalog_entries, :group_name
+  end
+end