fix: change products.canonical_name to TEXT, trim whitespace on import

VARCHAR(255) was too narrow for some OpenFoodFacts product names.
Switching to TEXT removes the length constraint entirely.
Also trim whitespace from resolved canonical names during import.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/migrations/001_initial_schema.sql

@@ -124,7 +124,7 @@ CREATE TABLE product_category_translations (
 -- ---------------------------------------------------------------------------
 CREATE TABLE products (
     id                UUID         PRIMARY KEY DEFAULT uuid_generate_v7(),
-    canonical_name    VARCHAR(255) NOT NULL,
+    canonical_name    TEXT         NOT NULL,
     category          VARCHAR(50)  REFERENCES product_categories(slug),
     default_unit      VARCHAR(20)  REFERENCES units(code),
     barcode           TEXT         UNIQUE,