[Lee-Juntong]

A negative result limit reaches SQLite as LIMIT -1, which removes the limit; other invalid limits and day windows produce inconsistent query behavior.

Validate windows before database discovery in read, search, recent, system-events, summary and stats. Require positive integer days and integer result limits from 1 to 2000; reject booleans and non-integers with a clear ValueError.

Validation: 54 invalid-input cases verify rejection before any database access, plus three valid limit boundaries. Invalid-input regressions fail on main and the updated suite passes. This changes only window validation.

Local validation uses Windows/Python 3.12 and synthetic fixtures. The consistency-checker file and two fingerprint-dependent existing tests were excluded by the local execution policy; no account databases, chat contents or keys are included.

Local branch suite: 138 passed, two tests deselected, consistency-checker file excluded.

[freanocank]

Thanks for the fix and regression tests. Adopted through #15 with your original commits preserved. Invalid windows and limits are rejected before database discovery; valid boundaries pass.

The combined suite passes all four macOS/Windows × Python 3.10/3.13 CI jobs; Windows reports 209 passed, and macOS reports 208 passed with the Windows-only test skipped.