Add import session save/restore

inventory-server/migrations/001_create_import_sessions.sql

@@ -0,0 +1,29 @@
+-- Migration: Create import_sessions table
+-- Run this against your PostgreSQL database
+
+CREATE TABLE IF NOT EXISTS import_sessions (
+  id SERIAL PRIMARY KEY,
+  user_id INTEGER NOT NULL,
+  name VARCHAR(255),                    -- NULL for unnamed/autosave sessions
+  current_step VARCHAR(50) NOT NULL,    -- 'validation' | 'imageUpload'
+  data JSONB NOT NULL,                  -- Product rows
+  product_images JSONB,                 -- Image assignments
+  global_selections JSONB,              -- Supplier, company, line, subline
+  validation_state JSONB,               -- Errors, UPC status, generated item numbers
+  created_at TIMESTAMP DEFAULT NOW(),
+  updated_at TIMESTAMP DEFAULT NOW()
+);
+
+-- Ensure only one unnamed session per user (autosave slot)
+CREATE UNIQUE INDEX IF NOT EXISTS idx_unnamed_session_per_user
+  ON import_sessions (user_id)
+  WHERE name IS NULL;
+
+-- Index for fast user lookups
+CREATE INDEX IF NOT EXISTS idx_import_sessions_user_id
+  ON import_sessions (user_id);
+
+-- Add comment for documentation
+COMMENT ON TABLE import_sessions IS 'Stores in-progress product import sessions for users';
+COMMENT ON COLUMN import_sessions.name IS 'Session name - NULL indicates the single unnamed/autosave session per user';
+COMMENT ON COLUMN import_sessions.current_step IS 'Which step the user was on: validation or imageUpload';