Add filter expression tests and fix tag OR syntax in hybrid queries

    - Add comprehensive test suite (test_filter_expressions.py) covering:
      * Tag filters with OR syntax (@field:{tag1|tag2|tag3})
      * Numeric ranges (9 variants: inclusive/exclusive bounds, infinity)
      * Logical negation, operator precedence, hybrid queries
      * 23 test cases validating parser correctness
    - Fix tag OR separator: use ‘|' instead of index separator

Author: zvi-code