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/v3.3_marketplace_any_part.sql

@@ -0,0 +1,91 @@
+-- ═══════════════════════════════════════════════════════════════════════
+-- v3.3 — Marketplace accepts any part number (seller listings)
+-- Target: nexus_autoparts (master DB)
+-- Date: 2026-05-17
+--
+-- Makes warehouse_inventory part_id nullable and adds seller-defined
+-- fields so any seller can list parts that don't exist in the OEM catalog.
+-- Existing OEM-matched listings are untouched.
+-- ═══════════════════════════════════════════════════════════════════════
+
+-- ─── 1. WAREHOUSE_INVENTORY — add seller listing columns ─────────────
+
+ALTER TABLE warehouse_inventory
+    ADD COLUMN IF NOT EXISTS seller_part_number VARCHAR(100),
+    ADD COLUMN IF NOT EXISTS seller_part_name   VARCHAR(300),
+    ADD COLUMN IF NOT EXISTS seller_category    VARCHAR(100),
+    ADD COLUMN IF NOT EXISTS tenant_inventory_id INTEGER;
+
+-- Make part_id nullable so seller listings (without catalog match) can exist
+ALTER TABLE warehouse_inventory ALTER COLUMN part_id DROP NOT NULL;
+
+-- ─── 2. WAREHOUSE_INVENTORY — drop old unique, add partial uniques ───
+
+-- The old constraint was on (user_id, part_id, warehouse_location).
+-- We replace it with two partial unique indexes:
+--   - OEM items:    (bodega_id, part_id, warehouse_location) WHERE part_id IS NOT NULL
+--   - Seller items: (bodega_id, seller_part_number, warehouse_location) WHERE part_id IS NULL
+
+ALTER TABLE warehouse_inventory
+    DROP CONSTRAINT IF EXISTS warehouse_inventory_user_id_part_id_warehouse_location_key;
+
+DROP INDEX IF EXISTS idx_wi_unique_composite;
+
+CREATE UNIQUE INDEX IF NOT EXISTS idx_wi_unique_oem
+ON warehouse_inventory(bodega_id, part_id, warehouse_location)
+WHERE part_id IS NOT NULL;
+
+CREATE UNIQUE INDEX IF NOT EXISTS idx_wi_unique_seller
+ON warehouse_inventory(bodega_id, seller_part_number, warehouse_location)
+WHERE part_id IS NULL;
+
+-- Ensure every row has either part_id or seller_part_number
+ALTER TABLE warehouse_inventory
+    DROP CONSTRAINT IF EXISTS chk_wi_part_or_seller;
+
+ALTER TABLE warehouse_inventory
+    ADD CONSTRAINT chk_wi_part_or_seller
+    CHECK (
+        (part_id IS NOT NULL AND seller_part_number IS NULL)
+        OR
+        (part_id IS NULL AND seller_part_number IS NOT NULL)
+    );
+
+-- ─── 3. WAREHOUSE_INVENTORY — search indexes ─────────────────────────
+
+CREATE INDEX IF NOT EXISTS idx_wi_seller_pn
+ON warehouse_inventory (bodega_id, seller_part_number)
+WHERE part_id IS NULL;
+
+CREATE INDEX IF NOT EXISTS idx_wi_seller_category
+ON warehouse_inventory (seller_category)
+WHERE part_id IS NULL;
+
+-- GIN index for text search on seller listings
+CREATE INDEX IF NOT EXISTS idx_wi_seller_search
+ON warehouse_inventory
+USING gin (to_tsvector('spanish',
+    COALESCE(seller_part_name, '') || ' ' || COALESCE(seller_part_number, '')
+))
+WHERE part_id IS NULL;
+
+-- ─── 4. PURCHASE_ORDER_ITEMS — make part_id nullable ─────────────────
+
+ALTER TABLE purchase_order_items
+    ALTER COLUMN part_id DROP NOT NULL;
+
+-- Add a flag so seller listings can be distinguished in POs
+ALTER TABLE purchase_order_items
+    ADD COLUMN IF NOT EXISTS is_seller_listing BOOLEAN NOT NULL DEFAULT FALSE;
+
+-- ─── 5. Back-compat: ensure existing rows are valid ──────────────────
+
+-- Existing rows should have part_id set and seller_part_number NULL.
+-- If any row violates the new check, this will fail loudly.
+UPDATE warehouse_inventory
+SET seller_part_number = NULL
+WHERE part_id IS NOT NULL AND seller_part_number IS NOT NULL;
+
+UPDATE warehouse_inventory
+SET part_id = NULL
+WHERE part_id IS NULL AND seller_part_number IS NULL;