feat: MercadoLibre integration + inventory bulk publish + WhatsApp bridge fixes

- Add MercadoLibre OAuth, listings, orders, webhooks and category search
- New marketplace_external_bp.py, meli_service.py, marketplace_external_service.py
- New marketplace_external.html/js with ML management UI
- Inventory: bulk publish to ML with category autocomplete, listing type and shipping selectors
- Inventory: new .btn--meli styles, select/label CSS fixes
- WhatsApp bridge: rate limiting, 440/515/408 error handling, stale watchdog
- DB migration v3.4_meli_integration.sql for marketplace_listings, orders, sync_queue
- Add Celery tasks for ML sync and webhook processing
- Sidebar: MercadoLibre navigation link

pos/migrations/v3.4_meli_integration.sql

@@ -0,0 +1,110 @@
+-- ============================================================
+-- v3.4 MercadoLibre Integration
+-- ============================================================
+-- Adds tables for external marketplace listings, orders,
+-- order items, and a generic sync queue.
+-- All tables live in the tenant DB.
+-- ============================================================
+
+-- Listings published on MercadoLibre (extensible to Amazon later)
+CREATE TABLE IF NOT EXISTS marketplace_listings (
+    id                  SERIAL PRIMARY KEY,
+    inventory_id        INTEGER REFERENCES inventory(id),
+    channel             VARCHAR(20) NOT NULL DEFAULT 'mercadolibre',
+    external_item_id    VARCHAR(50) NOT NULL,
+    external_status     VARCHAR(30) DEFAULT 'active',
+    external_permalink  TEXT,
+    title               TEXT,
+    meli_category_id    VARCHAR(30),
+    publish_price       NUMERIC(12,2),
+    last_sync_at        TIMESTAMPTZ,
+    sync_errors         TEXT,
+    is_active           BOOLEAN DEFAULT true,
+    created_at          TIMESTAMPTZ DEFAULT NOW()
+);
+
+CREATE INDEX IF NOT EXISTS idx_marketplace_listings_inventory
+    ON marketplace_listings(inventory_id);
+CREATE INDEX IF NOT EXISTS idx_marketplace_listings_external
+    ON marketplace_listings(external_item_id);
+CREATE UNIQUE INDEX IF NOT EXISTS idx_marketplace_listings_unique
+    ON marketplace_listings(inventory_id, channel) WHERE is_active = true;
+
+-- Orders received from MercadoLibre
+CREATE TABLE IF NOT EXISTS marketplace_orders (
+    id                  SERIAL PRIMARY KEY,
+    channel             VARCHAR(20) NOT NULL DEFAULT 'mercadolibre',
+    external_order_id   VARCHAR(50) NOT NULL UNIQUE,
+    external_status     VARCHAR(30) NOT NULL,
+    buyer_name          VARCHAR(200),
+    buyer_email         VARCHAR(200),
+    buyer_phone         VARCHAR(50),
+    buyer_nickname      VARCHAR(100),
+    shipping_address    JSONB,
+    total_amount        NUMERIC(12,2),
+    shipping_cost       NUMERIC(12,2),
+    meli_shipping_id    VARCHAR(50),
+    nexus_sale_id       INTEGER REFERENCES sales(id),
+    status              VARCHAR(20) DEFAULT 'pending',
+    notes               TEXT,
+    raw_json            JSONB,
+    created_at          TIMESTAMPTZ DEFAULT NOW(),
+    updated_at          TIMESTAMPTZ DEFAULT NOW()
+);
+
+CREATE INDEX IF NOT EXISTS idx_marketplace_orders_status
+    ON marketplace_orders(status);
+CREATE INDEX IF NOT EXISTS idx_marketplace_orders_external
+    ON marketplace_orders(external_order_id);
+
+-- Items inside a marketplace order
+CREATE TABLE IF NOT EXISTS marketplace_order_items (
+    id                      SERIAL PRIMARY KEY,
+    marketplace_order_id    INTEGER REFERENCES marketplace_orders(id) ON DELETE CASCADE,
+    inventory_id            INTEGER REFERENCES inventory(id),
+    external_item_id        VARCHAR(50),
+    title                   VARCHAR(300),
+    quantity                INTEGER NOT NULL,
+    unit_price              NUMERIC(12,2),
+    total_price             NUMERIC(12,2),
+    listing_id              INTEGER REFERENCES marketplace_listings(id)
+);
+
+-- Generic sync queue (reusable for future Amazon integration)
+CREATE TABLE IF NOT EXISTS marketplace_sync_queue (
+    id              SERIAL PRIMARY KEY,
+    inventory_id    INTEGER REFERENCES inventory(id),
+    channel         VARCHAR(20) NOT NULL,
+    action          VARCHAR(20) NOT NULL,
+    status          VARCHAR(20) DEFAULT 'pending',
+    payload         JSONB,
+    error_message   TEXT,
+    retry_count     INT DEFAULT 0,
+    created_at      TIMESTAMPTZ DEFAULT NOW(),
+    processed_at    TIMESTAMPTZ
+);
+
+CREATE INDEX IF NOT EXISTS idx_marketplace_sync_queue_pending
+    ON marketplace_sync_queue(status, channel) WHERE status = 'pending';
+
+-- Add source column to sales to track origin (POS, ML, Amazon, etc.)
+-- If the column already exists from another migration, do nothing.
+DO $$
+BEGIN
+    IF NOT EXISTS (
+        SELECT 1 FROM information_schema.columns
+        WHERE table_name = 'sales' AND column_name = 'source'
+    ) THEN
+        ALTER TABLE sales ADD COLUMN source VARCHAR(30) DEFAULT 'pos';
+    END IF;
+END $$;
+
+DO $$
+BEGIN
+    IF NOT EXISTS (
+        SELECT 1 FROM information_schema.columns
+        WHERE table_name = 'sales' AND column_name = 'external_order_id'
+    ) THEN
+        ALTER TABLE sales ADD COLUMN external_order_id VARCHAR(50);
+    END IF;
+END $$;