[BUG] Oracle instance status persistence uses an unsupported LIMIT clause #7724

Current behavior

InstanceInfoServiceImpl.createOrUpdate first executes InstanceInfoMapper.selectOneByQuery. Its only mapped statement ends with LIMIT 1 and has no Oracle-specific databaseId variant. Oracle does not support this syntax, so the instance persistence path cannot perform the identity lookup on an Oracle deployment.

The same mapper already has an Oracle-specific existed statement using ROWNUM = 1, demonstrating the available dialect pattern. Failure before the insert/update also interacts with the unguarded periodic persistence task tracked by #6496.

Source evidence

• selectOneByQuery including LIMIT 1
• Existing Oracle-specific lookup pattern
• Instance persistence call site

Confirmed mapped SQL shape by local XML inspection; no Oracle server was run during issue preparation.

Acceptance criteria

• Supply supported Oracle syntax for selectOneByQuery, preserving all identity/namespace predicates and single-row behavior.
• Retain working mappings for the other supported dialects.
• Validate Oracle mapped-statement selection and execute the instance lookup/create/update path on the supported Oracle test environment.
• Verify null/optional filters follow the existing query contract without broadening matches.
• Add regression coverage preventing generic LIMIT syntax from being selected for Oracle.

Related: #6496 covers scheduled task resilience and must not be treated as the SQL fix.