[MugdhoAI]

Summary

• Reject database files whose length is not an exact multiple of the 4096-byte page size.
• Add a dedicated pager corruption result for partial pages.
• Propagate this condition through table_open as SQLITE_CORRUPT.
• Add pager and database regression tests for truncated and oversized partial-page files.

Validation

• Local validation has not yet been run against this branch.
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Scope

This change does not alter the on-disk format for valid databases. It rejects malformed files that previously reached a short-read path and were reported as generic I/O failures.