Fix(pattern_match): prevent false positive when valid regex doesn't match

[Jean-Regis-M]

Summary

Fixes #129
Adds an early return for the case where a valid regex finds no match, preventing fallthrough to a literal substring check that could cause false positives.

Problem

When is_regex=True and the regex is valid but finds no match, _matches_pattern proceeds to a literal substring search using the raw regex string. If the text contains that raw string (e.g., the pattern appears literally), the function incorrectly returns (True, matched_text).

Root Cause

In _matches_pattern, after the regex search block (try/except), there is no explicit return for the “valid regex, no match” case. Execution falls through to the literal search logic, which treats the pattern as a plain substring.

Solution

Added return False, None inside the try block after checking for a match. This ensures that a valid regex with no matches returns immediately, bypassing the literal fallback. Invalid regex still falls through to literal matching (existing behavior).

Impact

• No breaking changes
• Minimal diff (one line added)
• Eliminates false positives for the described scenario
• All existing tests pass

Testing

• Added test case PRM-PAT-028 (provided in issue) passes.
• Ran all existing pattern match tests; they continue to pass.
• Manual verification of invalid regex fallback remains intact.