Fix UniqueException message to indicate unique index violation

[Copilot]

UniqueException was using the same "Document already exists" message as DuplicateException, making it impossible to distinguish between a duplicate document ID and a unique index constraint violation from the error message alone.

• Updated the UniqueException message to "Unique index violation" in all three adapters: MariaDB, SQLite, and Postgres
• DuplicateException messages remain unchanged as "Document already exists" is correct for that case

[greptile-apps]

Greptile Summary

Updates the UniqueException message from "Document already exists" to "Unique index violation" across all three adapters (MariaDB, Postgres, SQLite), making it distinguishable from DuplicateException's "Document already exists" message. The change is consistent across all adapters, the DuplicateException messages are correctly left unchanged, and existing tests check by instance type rather than message string so they remain unaffected.

Confidence Score: 5/5

Safe to merge — minimal, focused message-string change with no logic impact.

All three adapters are updated consistently, no detection logic was altered, and no tests check the literal message text. No P0/P1 findings.

No files require special attention.

Important Files Changed

Filename	Overview
src/Database/Adapter/MariaDB.php	Changed UniqueException message from 'Document already exists' to 'Unique index violation' at line 1805; DuplicateException messages unchanged.
src/Database/Adapter/Postgres.php	Changed UniqueException message from 'Document already exists' to 'Unique index violation' at line 1929; DuplicateException messages unchanged.
src/Database/Adapter/SQLite.php	Changed UniqueException message from 'Document already exists' to 'Unique index violation' at line 1258; DuplicateException messages unchanged.

_{Reviews (1): Last reviewed commit: "Fix UniqueException message to say 'Uniq..." | Re-trigger Greptile}