Escape wildcard characters in free-text memory search

[laceyp99]

Summary

q search currently passes user input directly into a LIKE pattern, so % and _ act as wildcards instead of literal characters.

Steps to reproduce

1. Create memories with content foo_bar and fooXbar.
2. Query GET /memories?q=foo_bar.

Expected behavior

Only the literal foo_bar record should match.

Actual behavior

Both records match because _ is treated as a wildcard.

Relevant code

• app/storage.py:174-177
• README.md:146-148
• docs/data_object_schema.md:287-291

Suggested fix

Escape % and _ before building the LIKE pattern, or use an ESCAPE clause.

Tests

Add a regression test covering literal % and _ in q values.