feat: add fuzzy word-order independent item search

[engahmed1190]

Implement multi-word search that finds items regardless of search term word order. Searching for "Blue Large" now correctly finds "Large Blue Plastic Widget".

Implementation details:

Backend (pos_next/api/items.py):

• Dual search strategy for optimal performance and compatibility
  1. Primary: MySQL fulltext boolean mode (MATCH AGAINST) with relevance scoring
  2. Fallback: Pattern-based LIKE search with AND logic between words
• Each word in the search query must match at least one field (item_code, item_name, or description)
• Words can appear in any order across any field
• Added _build_item_base_conditions() helper to centralize filter logic
• Extracted field list to ITEM_RESULT_FIELDS constant for reusability
• Search term deduplication prevents redundant LIKE predicates
• Alphanumeric normalization handles special characters in search terms
• Prefix matching for words ≥3 chars (+word*) and exact match for shorter tokens
• Limit boolean terms to 8 for query performance

Frontend (POS/src/utils/offline/items.js):

• Updated searchCachedItems() for consistent word-order independence
• Single-word queries use optimized IndexedDB index lookups (startsWithIgnoreCase)
• Multi-word queries filter JavaScript-side using Array.every() for AND logic
• Searches across item_code, item_name, description, and barcodes fields
• Fetches 5x limit for multi-word to ensure adequate filtered results

Technical notes:

• Boolean search depends on search_index fulltext index on Item doctype
• LIKE search provides compatibility when fulltext fails or is unavailable
• Both online and offline search use consistent word-order-independent logic

Fixes issue where multi-word searches required exact phrase order.

[engahmed1190]

Fixes #5